It seemed like a very promising cancer immunotherapy lead. CHO Pharma, in Taiwan, had discovered that it was possible to target solid tumours with an antibody against a cell-surface glycolipid called SSEA-4.1 This antigen is present during embryonic development, but not seen on human cells again — until they turn into cancer cells.2 The company turned to Lan Bo Chen, a recently retired Harvard pathologist, to help develop this work into an anti-cancer therapy for solid tumours. “It is highly reasonable to imagine that we can use SSEA-4, overexpressed on cancer cells, as a target for CAR-T,” says Chen, now in his role as senior technology advisor for CHO Pharma.
CAR-T therapy works by genetically engineering a person’s own T cells in such a way that they recognize and attack cancer cells. This involves creating a chimeric antigen receptor (CAR) from an antibody against a target on the cell. But CAR-T therapy was designed for blood cancers so it needs several adaptations to make it suitable for the treatment of solid tumours.3 The cells need to be directed to the site of the tumour, survive in the tumour’s local microenvironment, and act only on tumour cells, not on healthy cells nearby.
But, when Chen tried to create CAR-T cells against SSEA-4, he hit a few obstacles. First it took him a long time to get his hands on a humanized SSEA-4 antibody suitable for adaptation. When he finally had one, he still had to find a way to turn that antibody into a CAR. And then to insert the CAR into a human T cell using lentiviral transduction.
Not every lab is capable of creating CAR-Ts. It’s not only a matter of having access to the right equipment and facilities. According to Chen, lentiviral production is a skill that even scientists at top biotech companies find difficult. This means that creating CAR-T cells often involves a lot of trial and error and is very time-consuming. “We can do it, but it may take 3–5 years, or longer,” says Chen. “It’s the rate-limiting step.” Without CAR-T cells, the research is unable to proceed.
Chen started to search for a company that could take his SSEA-4 antibody and create CAR-T cells that selectively target and kill solid tumours bearing that signature. He needed to be sure he could get a functional CAR-T system, which limited him to companies with a good track record in this field. He was travelling back and forth between the United States and Taiwan, and it was during one of his stays in Taiwan that he first heard about a California-based company called ProMab Biotechnologies, which seemed to have the exact experience he was looking for. Not wanting to wait until he was back in the US, Chen called ProMab, where technical support scientist, Van Dang, picked up the phone.
Custom CAR-T creation
Chen's CAR-T requirement was exactly the type of request that ProMab regularly fulfils. “Our clients are researchers who are interested in advancing CAR-T therapy,” says Dang. Some, like Chen, are optimizing CAR-T for solid tumour targets, others are testing how CAR-T responds in the context of a drug treatment. Dang adds that some researchers are now also exploring how CAR-T can expand into new areas beyond cancer. “People are thinking of using CAR-T cells to treat autoimmune disorders,” she adds.
For requests like Chen’s, ProMab uses a customer-provided antibody as the basis to develop a CAR, then packages it into a lentivirus. “Generally, it takes us about two months to get it all ready and going,” says Dang. That’s a lot faster than the years Chen estimated his team would take.
As well as making custom CAR-T cells for clients, ProMab develops its own, based on a collection of more than 5,000 monoclonal antibodies, assembled over the last two decades. The company uses its antibodies to create off-the-shelf CAR-T cells for in-demand targets, and also to conduct its own CAR-T research.4,5 For some targets, ProMab has created CAR-NK cells, which are modified natural killer (NK) cells that are emerging as an alternative immunotherapy pathway.
ProMab’s CAR-T cells undergo a series of quality control steps. “Quality begins with the antibody,” says Vita Golubovskaya, director of research and development. She explains that Promab performs humanization, affinity engineering and extensive specificity testing to ensure quality of the CAR before further development. That includes measuring transduction efficiency and testing cytotoxicity and cytokine release against tumour cells expressing the CAR's antigen. After in vitro tests using cell models to demonstrate CAR specificity, CAR-T are then tested in vivo and evaluated for producibility.
"Several companies have partnered with us to use our CAR-T cells," says Golubovskaya. For example, a Californian biotech used them to test the functionality of an assay it had developed to assess the potency of immunotherapeutics,6 while a drug development company in Oklahoma wanted them to test an immunotherapy target for colorectal cancer.7
For CHO Pharma, ProMab was able to generate, test and validate a construct for expressing SSEA-4-targeting CARs on T cells. The next step for Chen’s team is to take this to the clinical trial stage, to find out whether SSEA-4 is indeed the key to making CAR-T therapy work against solid tumours. If not, they will move to the next potential antigen target. They would need new constructs for that, but outsourcing this resource-intensive process to an experienced partner like ProMab will speed up the research and development significantly.
ProMab‘s work goes further. “Our expertise in cell engineering goes beyond CAR-T cells," says CEO John Wu. “We can perform stable genetic manipulations with viral transduction or transient expression with mRNA in a large range of cell types, which enables us and our partners to address needs in oncology, immunology and beyond. It’s a very exciting time.”