Lymphoproliferative Responses to HIV-Specific Antigens in the HIV-Infected Pediatric Patient

Abstract 44

Introduction: The development of strong cellular immune responses to HIV-specific antigens has been associated with lower HIV RNA levels in HIV-infected adult patients. These adults typically have weak lymphoproliferative responses (LPR) to these antigens, despite viral suppression due to highly active antiretroviral therapy (HAART). The purpose of this experiment is to characterize LPR to HIV-specific antigens in HIV-infected pediatric patients.

Methods: Patients were recruited from the St. Christopher's Hospital Immunology Clinic after informed consent. PBMC were separated from whole blood on a Ficoll gradient. PBMC were then resuspended in media (RPMI-1640 w/ 10% human AB serum) and 100 µl were added to each well of a 96 well plate at a concentration of 10⁶ cells/ml. Cells were cultured in triplicate with medium alone, PHA, or the following HIV-specific antigens: gp160, p24, nef, and rev. After 6 days of incubation, cells were labelled with 1 µCi of [³H]thymidine per well and incubated for 12 to 18 hrs. Cells were harvested and [³H] incorporation measured by scintillation counting. Stimulation indices (SI) were determined. Elispot assays for IFN-γ, IL-4, and IL-10 were performed with the same antigens in parallel to the 4 most recent samples for which LPR were measured.

Results: LPR were performed on 12 patients. A patient was considered to have a significant response to an antigen if the SI was greater than 3. The chart below indicates the number of patients with significant responses. (Table) All antigenic-specific LPR were also identified by IFN-γ Elispot assay which also identified weaker but specific responses not identified by LPR. No IL-4 or IL-10 responses were noted to any antigens.

Table 1 No caption available

Conclusions: These HIV-infected children, like most adults, have weak LPR to HIV-specific antigens, despite HAART including those with undetectable HIV RNA. Preliminarily, Elispot assays appear to be more sensitive for identifying antigenic responses than LPR. In the Elispot assays performed, IFN-γ responses and the absence of IL-4 or IL-10 responses suggest that a Th1 response dominates. We intend to obtain samples from additional children and perform other assays of cellular immune function including chemokine measurements and further Elispot assays for cytokine production.