CAR III
Below I discussed Chimeric Antigen Receptor (CAR) T-cells and also pulled up a reply by Linda Eissenberg which taught me a lot. CAR T-cells are killer T-cells genetically modified to kill cells to which an antibody binds. I promised crazier ideas in later posts. One was the idea of further genetic modification of CAR T-cells. From Linda Eissenberg I learned that this idea is neither crazy nor new as it was described in an article published moreCAR than 6 years ago.
My thoughts on genetic modificatoin of CAR T-cells follow.
One is deletion of the TGF beta receptor gene. TGF beta1 is an important “don’t kill me” signal displayed by regulatory T-cells. Regulatory T-cells which infiltrate tumors are an important problem for the immunotherapy of cancer. My thought *was* that the approach of using antiTGF beta1 antibodies has not been tried in humans, because of serious side effects. Just now I learn (from an article published in 2024) that it has been tried without serious side effects or promising anti-tumor effects. I still think that deletion of genes of checkpoint receptors (don’t kill me signal receptors) might be useful. The reason is that treatment with inhibitors of all known checkpoints might cause autoimmunity problems. If the receptors in the CAR are deleted, other killer cells (including self reacting killer cells) are not affected.
Update: the CAR T-cells without checkpoint receptors are potentially dangerous. They might be self reacting and also might become leukemic. For these reasons it would be wise to add the gene for herpes TK which makes cells vulnerable to gabciclovir. It may also be wise to add the gene for herpes thymidine kinase to ordinary CAR T-cells as they might lead to leukemia in “very rare cases”
end update:
An important advantage of genetic modification compared to in vitro treatment is that the genetic modifications are not diluted as cells divide (and replicate their genes).
Another of my ideas is to prepare the CAR cells for reactive oxygen species (ROS think hydrogen peroxide) whcih are present in the microenvironment of solid tumors. Before I suggested doing this by treating them in vitro before infusing them. Here, I suggest deletion of the gene for KEAP1 a protein which inhibits cells’ Nrf2 activated anti-oxidant system. I think this might be worth doing (I definitely think that in vitro activation of the anti-oxidant system is worth trying).
Another idea which I thought was semi crazy was attempting to produce off the shelf CARs (that is CARs produced from a standard cell line and used for different patients ) instead of custom made CARs produced using the patient’s cells. Again, this is not novel – it was done and reported in the article to which Linda Eissenberg directed me.
Update: The linked article also stresses the importance of deleting the gene for a part of the natural T-cell receptor which is not replaced by the chimeric antigen receptor. This is important to prevent the off the shelf CAR from attacking the patient, that is to prevent graft versus host disease. This is definitely a necessarey step (and was sufficient in the case of acute lymphocytic leukemia describe in the linked article.
end update.
I still claim to have thoughts about how to make off the shelf CARs which will survive for a long time in the patient (I think such prolonged survival is needed to treat solid tumors but not to treat leukemia as in the article).
Cells are killed if they display novel antigens with the surface proteins HLA-A, HLA-B and HLA-C. These proteins vary across people and they (just the display protein “displaying” beta 2 microglobulin) are very important causes of transplant rejection.
I would consider deleting the HLA A B and C genes. There is a problem – there are cells called natural killer cells (NK cells) which kill cells which don’t display self HLA proteins. To prevent this, I would make cells produce large amounts of HLA-E which inhibits killing by NK cells. I learn that it would also be necessary to delete the cells non-chimeric T-cell receptor to prevent the infused CAR cells from attacking the patient (this is the way with which at least temporarily surviving off the shelf CARs were made in the linked article).
Another approach would be to modify the cells so that they display GARP (a protein which binds and activates latent TGF Beta1. Lacking the TGF beta1 receptor , they would not inactivate themselves but would inactivate the patients’ killer t-cells (and macrophages) which would otherwise kill them.
I do think that off the shelf CARs have promise.