Conditioning Regimens

Optimizing the use of anti-interleukin-6 monoclonal antibody with dexamethasone and 140 mg/m2 of melphalan in multiple myeloma: results of a pilot study including biological aspects

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Summary:

Interleukin-6 (IL-6) is a major survival factor for multiple myeloma (MM) cells preventing apoptosis induced by dexamethasone (DEX) or chemotherapy. In all, 24 consecutive patients with MM in first-line therapy received DEX for 4 days, followed by melphalan (HDM: 140 mg/m2) and autologous stem cell transplantation (ASCT). The anti-IL-6 monoclonal antibody (mAb) (B-E8) was given till haematological recovery, starting 1 day before DEX. Results were historically compared to MM patients treated with HDM 140 and 200 mg/m2. Our results show (1) that B-E8 was able to fully neutralize IL-6 activity in vivo before and after HDM as shown by inhibition of C reactive protein (CRP) production; (2) no haematological toxicity; (3) a significant reduction of mucositis and fever; (4) a median event-free survival of 35 months and an overall survival of 68.2% at 5 years with a median follow-up of 72 months; and (5) the overall daily IL-6 production progressively increased on and after 7 days post-HDM, with the increased serum CRP levels. In the 5/24 patients with uncontrolled CRP production, a large IL-6 production was detected (320 μg/day) that could not possibly be neutralized by B-E8. These data show the feasibility to neutralize IL-6 in vivo with anti-IL-6 mAb in the context of HDM.

Main

Multiple myeloma (MM) is still an incurable disease despite the fact that high-dose melphalan (HDM) increases the complete response rate five- to six-fold, leading to a significant increase of the median survival, from 44 months with conventional chemotherapy to 57 months with HDM.1, 2, 3, 4 The standard HDM is a combination of melphalan 140 mg/m2 plus total body irradiation (TBI) or melphalan 200 mg/m2,2, 5 both associated with increased toxicity for older patients.6 Tandem HDM has been tested with major improvement of response rate in Phase II studies7, 8, 9 and potent survival benefit in a randomized Phase III study.4 A reduction of tumour contamination of the autograft, using purification of CD34 peripheral blood stem cells (PBSC) is feasible,10, 11 but did not improve survival in a randomized study.12

Interleukin-6 (IL-6) is a major myeloma survival factor in vitro.13, 14 In particular, anti-IL-6 monoclonal antibodies (mAb) can block the proliferation of primary myeloma cells in short-term culture 15, 16 and IL-6-dependent myeloma cell lines can be reproducibly obtained from MM patients with extramedullary proliferation.17 In vivo, IL-6 is overproduced by the tumour environment in MM patients18 and serum levels of IL-6 and soluble IL-6 receptors are increased in association with a poor prognosis.19, 20 Thus, anti-IL-6 mAb can be useful to induce myeloma cell apoptosis.

We have previously found that treatments of patients with terminal disease with anti-IL-6 mAb can block the in vivo proliferation of myeloma cells and reduce IL-6-related toxicities (ie fever, cachexia).21, 22, 23 A limitation of the anti-IL-6 treatments was the very large production of endogenous IL-6 in some patients with MM that could not be neutralized by the anti-IL-6 mAb.24, 25

As blocking IL-6 can increase the apoptosis of myeloma cells induced by dexamethasone (DEX)26 and the drug sensitivity of tumour cells,27, 28 we have investigated the possibility of treating patients having MM with the B-E8 anti-IL-6 mAb, high dose of DEX (40 mg/day for 4 days), and high dose of melphalan (140 mg/m2) supported by autologous stem cell transplantation (ASCT). The anti-IL-6 mAb was given before and during DEX-HDM to potentiate the apoptotic effect of DEX and HDM. It was also administered for 15 days after HDM to block the production of IL-6 occurring after HDM in association with haematopoietic recovery. Indeed, the production of IL-6 that occurs after HDM might favour the survival, reparation and growth of the minor fraction of myeloma cells that are not destroyed by HDM. We found that prolonged anti-IL-6 treatment in association with DEX and HDM was feasible, did not affect haematopoietic recovery but reduced HDM-related toxicities. In addition, using the original methodology developed by our group,24, 29, 30 we demonstrated for the first time a dramatic increase in IL-6 production after HDM. These data confirm the potential importance to block IL-6 that is a main myeloma cell survival factor, to avoid the rescue of some myeloma cells after HDM.

Patients and methods

Patients treated with anti-IL-6 mAb

In all, 24 consecutive patients with newly diagnosed MM and justifying a high-dose therapy were included in this study, after written informed consent and the agreement of the ethical committee of Montpellier University Hospital. All of them had standard evaluation, including MRI, particularly for defining high-risk patients with stage I DS, and having multifocal lesions. These patients had four courses of standard VAD (vincristine 0.4 mg/day and doxorubicin 9 mg/m2/day for 4 days by continuous i.v. route and DEX 40 mg/day at days 1–4, 9–12 and 17–20) after diagnosis. Then, patients received cyclophosphamide (4 g/m2), followed by administration of granulocyte colony stimulating factor (Neupogen*, Amgen-Roche, Paris France) at 5 μg/kg/day, starting 3 days after cyclophosphamide until collection of PBSC.

The 24 patients received B-E8, an IgG1 murine monoclonal directed against IL-6, prepared by Diaclone Besançon, France, as previously described.21, 22 The patients received DEX (40 mg/day from day −5 to −2), HDM (140 mg/m2, at day −2), followed by transplantation of autologous PBSC at day 0. They received 200 mg of anti-IL-6 at day −6 followed by 20 mg/day from day −5 until haematological recovery, corresponding to white blood cell count superior to 106/l. B-E8 was diluted in 100 ml saline serum with 0.5% human albumin (LFB, Les Ullis, France) and then administered as a 1-h infusion every day, at the same time. The dose was chosen according to previous clinical results and pharmacological data.21, 22, 23, 24, 25

From day −6 until haematological recovery corresponding to the last B-E8 injection, patients were hospitalized in the same transplantation unit with standard treatment used in aplasia, including i.v. antibiotics (cefpirome 2 g × 2 and netilmicine 150 mg × 3/day, plus vancomycin 500 mg × 6/day in case of infection and/or appearance or persistence of fever after 48 h of standard antibiotics, ceftazidim or imipenem-cilastine and/or amphotericin B, being the third-line therapy) started as soon as aplasia (less than 500/mm3 neutrophils) occurred, which corresponds to day −3 or −4 after autologous transplantation.

Patient's population with matched prognostic factors

From 01/1995 to 05/2001, 167 consecutive MM patients were treated by HDM supported by ASCT in our department (Haematology-Oncology, University Hospital, Montpellier, France). HDM included 140 mg/m2 melphalan for older patients, 200 mg/m2 melphalan or 140 mg/m2 melphalan plus TBI for younger patients, or B-E8 anti-IL-6 mAb, DEX and 140 mg/m2 melphalan in the current study (anti-IL-6-DEX-HDM140 group). We selected two groups of MM patients with matched prognostic factors as compared with the anti-IL-6-DEX-HDM140 group included in this study, one group of 25 patients treated with 140 mg/m2 melphalan (HDM140 group) and one group of 24 patients treated with 200 mg/m2 melphalan (HDM200 group). Comparisons were made for response and tolerance.

C reactive protein evaluation after HDM in patients with MM

In order to evaluate the duration of IL-6 overproduction in MM patients treated with HDM (200 mg/m2), serum C reactive protein (CRP) levels were measured in 27 MM patients for 15 days after HDM. These patients had no major infection during aplasia. Of the 27 patients, 20 presented with fever 38°C for less than 4 days. The clinical parameters of these 27 patients were similar to those treated with anti-IL-6 mAb, in terms of age (median 62 years, range: 35–68 years) and haematological recovery (mean duration of neutropenia 12±2 days, for neutrophils <0.5 × 106/l and thrombopenia 13±2 days, for platelet counts <20 × 106/l).

Evaluation of clinical and standard biological response

All the patients had standard clinical and biological follow-up, including haematological parameters with blood cell counts and measurements of CRP levels every day, and creatinine, and liver tests, checked every 2 days in the serum. Blood, urine and other samples were tested for identification of infectious organisms if necessary. All the patients had an evaluation of the disease, which included bone marrow aspirate, electrophoresis and immuno-electrofixation of proteins in serum and urine, creatinine, β2 microglobulin, calcium, white blood cell count, and CRP and Ig measurement in the serum, at diagnosis, at the inclusion, 90 days after ASCT, every 6 months or when clinical events were observed. X-ray evaluation was performed at diagnosis, at the inclusion and 3 months after the end of treatment. MRI imaging of the spine and iliac bones was performed at the same periods and every year or in case of clinical progression.

Response was evaluated 90 days after autologous transplantation by using standard criteria31 and additional definition of very good partial response (VGPR), as previously mentioned.2, 4

Determination of plasma IL-6 and B-E8 mAb concentrations

Two anti-IL-6 mAb (AH-65 as a capture mAb and B-E4 as a detector mAb) were used in an ELISA to determine the concentration of plasma IL-6 as previously described.23, 24 These anti-IL-6 mAb recognized different epitopes on the IL-6 molecule from the epitope recognized by the B-E8 mAb injected into the patients. B-E8 mAb concentrations were also assayed by an ELISA.32

Calculation of daily IL-6 production in vivo

We used a mathematical model previously developed to calculate total IL-6 production in patients receiving anti-IL-6 mAb.24 In brief, at the concentration of anti-IL-6 mAb reached in the patients' plasma, all circulating IL-6 is bound to the anti-IL-6 mAb in the form of monomeric complex with a half-life of 3–4 days similar to that of the free antibody. In these patients treated with anti-IL-6 mAb, IL-6 is no longer eliminated by the kidneys or consumed by cells in vivo due to the blockage of its binding to IL-6R. Thus, knowing the amount of anti-IL-6 mAb injected daily and the fluctuations of the concentrations of the free anti-IL-6 mAb and of the IL-6/anti-IL-6 mAb immune complexes, the overall production of IL-6 on day ‘n’ in the whole organism can be estimated by the formula: IL-6 production on day ‘n’=2 × M × b((IL-6n)−b × (IL-6n−1))/{((Mn)−b × (Mn−1)) × (1+b)} as indicated before.23 In this formula, M, (IL-6n), (IL-6n−1), (Mn) and (Mn−1) are, respectively, the daily amount of injected mAb, the IL-6 concentration on day n, the IL-6 concentration on day n−1, the mAb concentration on day n and the mAb concentration on day n−1, respectively. ‘b’ is a coefficient dependent on the half-life of the mAb (b=e−(ln2)/(half-life of MAb)). If IL-6 biological activity is not completely blocked in an anti-IL-6-treated patient (in the case of partial blockage of CRP for example), the true overall IL-6 production in vivo is superior to the production estimated by this method.

Statistical methods

Comparisons between the groups of patients (anti-IL-6-DEX-HDM140 group and HDM140 and HDM200 historical control groups) in terms of demographic, efficacy, and safety data were performed using the two-sample t-test or Wilcoxon rank sum test. Overall survival (OS) and event-free survival (EFS) were calculated from the date of diagnosis and from the date of transplant, and summarized using Kaplan–Meier curves.33

Results

Serum CRP levels in MM patients treated with HDM

Figure 1 shows the mean serum CRP levels of 27 patients with MM treated with HDM. The mean CRP levels progressively increased following HDM with a peak observed on day 12 after the ASCT. In all, 21/27 patients had fever of more than to 38°5 during aplasia with a correlation between CRP and fever when it was more than this level. The level of CRP was associated with fever and additional signs including mucositis or other symptoms (data not shown). As CRP production is induced by IL-6 in vivo,15 these data suggest an increase in IL-6 production after HDM in these patients with MM.

Figure 1
figure1

Serum CRP levels after high-dose melphalan and ASCT in patients with multiple myeloma. Data are mean values of plasma CRP for 27 patients.

Patients

In Table 1 is presented a comparison of the clinical characteristics of the group of 24 MM patients treated with anti-IL-6-DEX-HDM140 and two control groups of MM patients with matched prognostic factors treated with either HDM140 or HDM200. Patients' characteristics were identical in the three groups, except for a higher age of patients receiving HDM140 as mentioned in Table 1. In all, 13/24 patients had detectable CRP serum level at the inclusion (15.5±6.9 mg/l). The 24 patients received 5.16±1.64 × 106 CD34+ cells/kg (Table 2). Patients in the two control groups received ASCT with similar numbers of CD34+ cells × 106/kg (4.24±1.30 and 4.40±1.57, respectively, in the HDM140 and HDM200 groups). Duration of anti-IL-6 mAb treatment was dependent on haematological recovery; that is, neutrophil count >0.5 × 106/l, platelet count >20 × 106/l, and transfusion independency. The median duration of anti-IL-6 treatment was 17 days (range 18–26 years).

Table 1 Clinical characteristics of the patients treated by anti-IL-6 mAB, DEX andHDM140, HDM140 and HDM200
Table 2 Haematological recovery and toxicity in the three groups of patients (ie, anti-IL-6, DEX and HDM140, HDM140 and HDM200)

Clinical evaluation

Feasibility and toxicity

No toxic death, toxicity, or allergic incidents were observed in patients treated with anti-IL-6 mAb, DEX and HDM140. As mentioned in Table 2, the number of infectious episodes was not different from those observed in the two control groups of patients who did not receive anti-IL-6 mAb. We observed two septicaemias (that were rapidly controlled) as compared to one septicaemia for both control groups. No pulmonary infections were observed in the group of patients treated with anti-IL-6 mAb as compared to, respectively, six episodes and one episodes in the two control groups. No delay for diagnosing infectious episodes was observed, with no difference of duration for antibiotics administration between anti-IL-6 mAb-treated patients and control patients. Of interest, the anti-IL-6 treatment reduced some HDM-related toxicities. Mucositis was significantly less frequent (5/24, 20%) in the group of patients treated with anti-IL6 mAb as compared to the two control groups (13/25, 52%) for HDM140 patients and 18/22 (82%) for HDM200 patients, P<0.001 (Table 2). In addition, mucositis was at a lower grade of toxicity (grade 2: 5/24 with no morphin infusion in the group of patients receiving anti-IL-6) as compared to 5/13 and 8/18 patients having grades 3–4 mucositis with morphin infusion in the groups of, respectively, HDM140 and HDM200 patients. The number of patients who experience nausea/emesis episodes WHO grade 2 was also lower in the group of anti-IL-6 mAb-treated patients: 2/24 patients (6%) as compared to 6/25 patients treated with HDM140 (24%) and 9/24 for the patients receiving HDM200 (37%, P<0.05). The number of days with fever (38°5) was lower and associated with a reduction in temperature degree (median: 4 vs 8 days, P<0.05). A higher number of patients having diarrhoea WHO grade less than three was observed in the group of patients having anti-IL6 mAb (four patients) as compared to the group treated by HDM140 (one patient, P<0.05) but not different from the group of patients treated by HDM200 (four patients). Thus, blocking IL-6 reduced some HDM-related toxicities, resulting in a better quality of life, particularly for oral intake and daily activity during aplasia.

Haematopoietic recovery

Blocking IL-6 before and after HDM did not delay neutrophil or platelet recoveries compared to MM patients treated with HDM alone, as indicated by the duration of aplasia and hospitalization and transfusion need (Table 2). This is of particular interest because IL-6 is a haematopoietic cytokine that is involved in megakaryopoiesis. In addition, patients with anti-IL-6 mAb had significantly less transfusion of red blood cell units when compared to the other control groups (1 vs 2, P<0.01), during the aplasia period, and the time of follow-up, except if any other treatment was administered.

Clinical response

Clinical response was evaluated according to criteria previously defined.29 Out of the 24 patients treated with anti-IL-6-DEX-HDM140, 13 (54%) were in CR (four patients) or in VGPR (nine patients). Six patients were in PR and five had a minimal response. OS and progression-free survival are shown in Figure 2. Median EFS was 35 months, and overall-free survival was 68.2% at 5 years, with a median follow-up 72 months.

Figure 2
figure2

Overall survival in patients treated by anti-IL-6 mAB, DEX, HDM140 and ASCT and patients treated with HDM140 or HDM200 and ASCT.

Biological evaluation

Determination of serum CRP, anti-IL-6 mAb and IL-6 concentrations

Daily serum CRP levels were evaluated in 16 out of the 24 patients treated with anti-IL-6 mAb. They decreased and were undetectable from day −2 to 6 for all the patients as shown in Figure 3. For three patients (patients 11, 18 and 20), CRP levels were again detectable from day 8 to 13 of treatment despite the daily injection of the anti-IL-6 mAb.

Figure 3
figure3

Serum CRP levels in patients treated with anti-IL-6 mAB, DEX, HDM140 and ASCT.

The concentration of circulating anti-IL-6 mAb was evaluated in 14 patients. As shown in Figure 4, the serum anti-IL-6 mAb concentration reached a maximum 1 day after the first injection of a charge dose of anti-IL-6 mAb (200 mg). The day −5 mAb concentration varied among the patients from 50 to 90 μg/l, likely as a reflect of a patient's variability of the diffusion volume. Then, following the injection of a daily dose of anti-IL-6 mAb, the plasma mAb concentration decreased progressively and stabilized on and after day 10 (average: 25.3 μg/l, range 12–36 μg/l).

Figure 4
figure4

Anti-IL6 serum concentration in patients treated with anti-IL-6 mAB, DEX, HDM140 and ASCT.

Serum IL-6 was measured with an ELISA detecting free IL-6 as well as IL-6 bound to B-E8 mAb. As shown in Figure 5, a low concentration of circulating IL-6 (average 0.33 ng/ml; range: 0.02–2.58 ng/ml) was detected before treatment in 13 out of the 13 patients tested. A slow increase in serum IL-6 was observed from day −5 to 0, followed by a more rapid increase after day 0 with a peak between days 7 and 12 (range: 2.36–52.10 ng/ml). This serum IL-6 was actually bound to the B-E8 (data not shown).

Figure 5
figure5

Serum IL-6 concentration in patients treated with anti-IL-6 mAB, DEX, HDM140 and ASCT.

Calculation of daily IL-6 production

The daily in vivo production of IL-6 was calculated in 14 patients treated with anti-IL-6 mAb using the mathematical model we described before.23 The median daily in vivo IL-6 production for the 14 patients is shown in Figure 6. This daily in vivo production was very low (<0.35 μg/day) from day −5 to −2 and increased progressively from day-0 till day-8. A wave of IL-6 production appeared in all patients between day 7 and 13 (median value of 35 μg/day, that is >100-fold increase compared to pretreatment values). This in vivo IL-6 production wave preceded WBC and platelet recovery with a 4- and 10-day delay, respectively. In Figure 7 are shown the mean values of IL-6 production for 5-day periods in the 14 patients. In five patients (P6, P11, P14, P18 and P20), high daily production of IL-6 was detected (median 320 μg/day, range 192–3350), with a median value of IL-6 production between day 6 and 10 superior to 50 μg (high-IL-6 producers). Three of them (patients 11, 18 and 20) had uncontrolled CRP production with serum CRP again detectable during anti-IL-6 treatment as shown on Figure 3. All of these five patients progressed within 18 months after autologous transplantation, and two of them died rapidly with fulminating disease. All of these patients had detectable plasma cell labelling index (1.5%, range 1.5–3.6%) and β2 microglobulin serum levels superior to 3.0 μg/ml. The ratio of mAb/IL-6 serum concentration was inferior to 250 for these three patients. We have previously shown that the B-E8 anti-IL-6 mAb was no longer able to block gp130 IL-6 transducer activation induced by IL-6 when the mAb/IL-6 ratio was less than 250.29

Figure 6
figure6

Median values of daily IL-6 production (μg/day) in patients treated with anti-IL-6 mAB, DEX, HDM40 and ASCT.

Figure 7
figure7

Daily IL-6 production (μg/day) measured at different times (day −5 to 0, day 1 to 5 and day 6 to 10) in patients treated with anti-IL-6 mAB, DEX, HDM140 and ASCT.

Discussion

In this study, we have demonstrated three points: (1) the occurrence and the quantification of an important wave of IL-6 production starting after HDM and ASCT; (2) the ability to block this wave of IL-6 production with anti-IL-6 mAb in a majority of patients; (3) the lack of obvious side effects of the anti-IL-6 mAb treatment in association with high-dose DEX, HDM and ASCT. On the contrary, anti-IL-6 mAb reduced some HDM-related toxicities. In addition, our data suggest a link between patients' potential of IL-6 production and their response rate following HDM supported by ASCT.

Regarding the first point, increased plasma levels of IL-6 after high-dose chemotherapy and PBSC were previously documented.34 Plasma IL-6 is only a small part of IL-6 produced in vivo that is mainly consumed by cells and rapidly eliminated by kidney with a 10 min half-life.29 In the present study, we were able to estimate the overall IL-6 production in vivo in patients treated with anti-IL-6 mAb. Indeed, the anti-IL-6 mAb captures IL-6 and induces it to circulate in the form of stable monomeric complexes with a 3–4 day half-life.29 Using this observation, the daily overall production of IL-6 could be estimated according to the methodology we previously developed.24 A median IL-6 production of 0.32 μg/day (range 0–1 μg/day) was found in these patients before DEX-HDM. After HDM and ASCT, median IL-6 production increased progressively 100-fold with a peak of 36 μg/day (range 9–246 μg/day). In two patients, it was superior to 100 μg/day. These were close to the doses of recombinant IL-6 known to have biological activity in vivo (ie 5 μg/kg/day).35

The second finding of this study is the feasibility to neutralize IL-6 with the B-E8 anti-IL-6 murine mAb before and after DEX and HDM treatment and ASCT. The B-E8 mAb has a high affinity with IL-6 (1011M) and was previously shown to block IL-6 activity in patients with MM, renal cell carcinoma, Castleman's disease and transplantation-related B cell lymphoma.22, 36, 37, 38 An interesting feature of B-E8 mAb is the low occurrence of human antibodies able to neutralize and clear B-E8 mAb. In a series of 15 patients with MM or renal cancer treated with B-E8 mAb, a clearance of B-E8 and escape from the treatment was found in only three of 15 patients, due to the occurrence of human antibodies to murine Fc fragments.39 In the other patients, the B-E8 mAb was given for several weeks without clearance or blockage of its activity. In the present study, the rare occurrence of human antibodies to B-E8 mAb should have been prevented due to the profound immuno-suppression induced by HDM. The efficacy of the anti-IL-6 mAb was shown by the complete blockage of CRP production in the majority of patients. CRP is an acute phase protein produced by hepatocytes whose production is strictly under the control of IL-6 in vitro40 and in vivo as demonstrated by our group. Indeed, we have shown that in vivo CRP production was completely blocked in a patient treated with B-E8 anti-IL-6 mAb for 2 months.21 Serum CRP was again detectable at the end of the treatment. A complete control of CRP production by IL-6 in vivo was subsequently confirmed in IL-6-knockout mice or other clinical trials with anti-IL-6 mAb.41 In the current study, CRP levels were undetectable in all 16 evaluated patients until day 6 after HDM. After 6 days post-HDM, CRP was again detectable in three out of 16 patients and progressively increased in these three patients despite the continuous infusion of anti-IL-6 B-E8. The daily IL-6 production was estimated in two of these three patients, and these two patients were actually those with a very high wave of IL-6 production (>100 μg/day). With such a high IL-6 production, we previously estimated that the antibody was unable to neutralize IL-6 activity in vivo.24 Given the blockage of CRP production, one can consider that the anti-IL-6 mAb was able to block completely IL-6 activity before and after HDM and ASCT in a great majority of patients.

The third finding is the lack of toxicity of the anti-IL-6 mAb treatment in these patients treated with DEX from day −5 to −2 before ASCT and HDM at day −2. As emphasized above, we decided to inject DEX before HDM in order to optimize the destruction of myeloma cells. Indeed, the blockage of IL-6 can dramatically increase myeloma cell apoptosis induced by DEX and by HDM in vitro. We found no delay in haematopoietic reconstitution and no increase in the transfusion need in the anti-IL-6-DEX-HDM140 group compared to groups of MM patients treated with the same dose of HDM and grafted with the same amount of CD34 progenitor cells. Thus, despite the fact that IL-6 can increase the growth of haematopoietic stem cells,42 and, in particular, speed up platelet reconstitution,43 other cytokines are likely produced in these patients, making a rapid recovery of platelet and neutrophil counts possible. Another interesting observation is the decrease of HDM and ASCT toxicities. Patients have less mucositis, and in particular no grade 3–4 mucositis. It is not possible here to ascertain whether this decreased toxicity is due the blockage of IL-6 activity for 15 days after HDM and ASCT or to DEX injection for 4 days before HDM and ASCT. This needs to be further investigated in patients treated with DEX-HDM alone or patients treated with anti-IL-6-DEX-HDM. The number of days with fever was reduced by half in the anti-IL-6-treated patients. This is not surprising because IL-6 is a pyrogenic cytokine and this was already observed in previous clinical studies with anti-IL-6 mAb.36, 38 Altogether, the quality of life was improved in the anti-IL-6-DEX-HDM140 group of patients.

There is a suggestion in this study for a link between the patient potential of IL-6 production and their response rate following DEX-HDM and autologous transplantation, with a rapid progression for the highest producers of IL-6. Furthermore, there is a suggestion for a clinical benefit with an apparent prolonged EFS, as compared to that observed in the literature, from 28–31 to 35 months.2, 4 It is important to stress that we documented here for the first time a 100-fold increase of the overall median IL-6 production in vivo after HDM and PBSC graft. According to several in vitro data, this very large in vivo IL-6 production may contribute to the rescue of the few myeloma cells that have escaped from HDM. Indeed, IL-6 may reduce melphalan-induced DNA damages in human myeloma cells.44 One mechanism could be its effect on genetically altered myeloma cells,45 eventually an increase of glutathione S-transferase π as observed in renal cell carcinoma cell lines.28 This possible rescue of chemotherapy-treated tumour cells by IL-6 may explain why serum IL-6 levels postautologous transplantation were shown to be predictors of poor response after high-dose chemotherapy and autologous transplantation in various cancers.46 We also have to emphasize that the anti-IL-6 mAb might have potentiated the apoptotic effect of DEX given just before HDM since numerous studies have shown that IL-6 can block the DEX-induced apoptosis of myeloma cells in vitro. This was the reason why we decided to inject DEX just before HDM treatment.

We are interested in pursuing this approach in four directions. First, the use of chimeric or humanized anti-IL-6 mAbs with a long half-life (3 weeks instead of 3–4 days) could prevent a daily injection of the mAb and makes it possible to increase the concentration of circulating mAb in vivo, especially in high-IL-6-producer patients. Chimeric or humanized antibodies with a very high affinity with IL-6 are now available from different sources.36 Secondly, we are interested in investigating the contribution of DEX treatment before HDM together with anti-IL-6 mAb treatment. Thirdly, it could be important to prolong the anti-IL-6 treatment for at least 1 month after ASCT in order to cover the wave of IL-6 production. Our goal is to block IL-6 as long as possible to push a maximum of melphalan-damaged myeloma cells to apoptosis. A simple indicator will be to completely block CRP production for 1 month after ASCT. In the present study, the treatment was stopped at haematopoietic recovery because we did not know the amount and duration of IL-6 production. Fourthly, it should be interesting to associate anti-IL-6 treatments with an intermediate high dose of melphalan (140 mg/m2) for elderly patients, or to use a repeated intermediate high dose of melphalan, to increase the dose of melphalan above 200 mg/m2 as performed by the group from Nantes,47 or to add other active drug to this combination.

In conclusion, the current study demonstrates the feasibility and the interest in blocking the large wave of IL-6 production that occurs after DEX-HDM and ASCT in order to reduce transplant-reduced toxicities and to avoid repair of HDM-damaged residual myeloma cells.

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Correspondence to J-F Rossi.

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Keywords

  • anti-interleukin-6
  • multiple myeloma
  • autologous transplantation

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