Adoptive cell therapies in cancer arose from an urgent need to improve on prevailing state-of-the-art cancer Rx. Being relatively non-specific, Rx such as radiation and chemotherapy tend to inflict considerable collateral cost, damaging or killing healthy tissues as well.
Cancers have two key attributes that lend themselves to adoptive cell therapies.
- Cancer-specific cell-surface molecules, i.e., those specifically expressed by cancers and not by normal cells.
- Adoptive cell therapies simply take advantage of this fact.
- For example, CAR-T (Chimeric Antigen Receptor-T) cells are T cells genetically engineered to express a receptor that specifically binds a cancer cell-surface molecule. This makes these T cells stick to the cancer cells. Such close interaction with cancers is in turn crucial to activate cancer-specific T cells.
- Currently possible only for B cell cancers. Many companies and academic groups are racing to try and find specific molecules expressed by solid cancers that could also guide specific T cell responses to them.
- With such cancer-specific molecules red rags and anti-cancer T cells the bulls, adoptive cell therapies are better than radiation and chemotherapy at targeting cancer cells while sparing healthy cells.
- Cancers are typically chronic.
- Adoptive cell therapies are personalized medicine and typically take time to prepare, anything from weeks to months.
- They entail isolation of immune cells from patients, extended periods of in vitro culture and genetic engineering before being infused back into the patients.
Infectious diseases differ from cancer in the two key attributes of specificity and time.
- Adoptive cell therapies for cancers can directly target them. This isn’t possible for infectious disease agents.
- Be they bacteria or viruses, infectious disease agents typically invade our cells and reside within.
- Typically they don’t replicate freely outside our cells.
- Thus, while infectious disease agents do express unique molecules, they can’t present them directly to T cells, only to B cells and their antibodies. This is the principle behind the old approach of infusing infectious disease patients with from convalescing or recovered patients.
- This is a difference in kind between infectious disease agents and cancers because the latter can process and present their molecules directly to T cells.
- Infectious diseases are typically acute.
- Their Rx needs to be rapid and fast-acting.
- Patients can’t wait the weeks or months it takes to generate patient-specific adoptive cell therapies.
There is also the question of need. Unlike cancer, prevailing infectious disease Rx such as antibiotics, antivirals and antibodies are already quite specific and don’t inflict such a high price in collateral cost that we see with radiation and chemotherapy.