Affinity fine-tuning anti-CAIX CAR-T cells mitigate on-target off-tumor side effects

One of the major hurdles that has hindered the success of chimeric antigen receptor (CAR) T cell therapies against solid tumors is on-target off-tumor (OTOT) toxicity due to sharing of the same epitopes on normal tissues. To elevate the safety profile of CAR-T cells, an affinity/avidity fine-tuned CAR was designed enabling CAR-T cell activation only in the presence of a highly expressed tumor associated antigen (TAA) but not when recognizing the same antigen at a physiological level on healthy cells. Using direct stochastic optical reconstruction microscopy (dSTORM) which provides single-molecule resolution, and flow cytometry, we identified high carbonic anhydrase IX (CAIX) density on clear cell renal cell carcinoma (ccRCC) patient samples and low-density expression on healthy bile duct tissues. A Tet-On doxycycline-inducible CAIX expressing cell line was established to mimic various CAIX densities, providing coverage from CAIX-high skrc-59 tumor cells to CAIX-low MMNK-1 cholangiocytes. Assessing the killing of CAR-T cells, we demonstrated that low-affinity/high-avidity fine-tuned G9 CAR-T has a wider therapeutic window compared to high-affinity/high-avidity G250 that was used in the first anti-CAIX CAR-T clinical trial but displayed serious OTOT effects. To assess the therapeutic effect of G9 on patient samples, we generated ccRCC patient derived organotypic tumor spheroid (PDOTS) ex vivo cultures and demonstrated that G9 CAR-T cells exhibited superior efficacy, migration and cytokine release in these miniature tumors. Moreover, in an RCC orthotopic mouse model, G9 CAR-T cells showed enhanced tumor control compared to G250. In summary, G9 has successfully mitigated OTOT side effects and in doing so has made CAIX a druggable immunotherapeutic target.

Analyzing Angiotensin II Receptor Type 1 Clustering in PC12 Cells in Response to Hypoxia Using Direct Stochastic Optical Reconstruction Microscopy (dSTORM)

Angiotensin II (Ang II) is a hormone that plays a major role in maintaining homeostasis. The Ang II receptor type 1 (AT₁R) is expressed in acute O₂ sensitive cells, including carotid body (CB) type I cells and pheochromocytoma 12 (PC12) cells, and Ang II increases cell activity. While a functional role for Ang II and AT₁Rs in increasing the activity of O₂ sensitive cells has been established, the nanoscale distribution of AT₁Rs has not. Furthermore, it is not known how exposure to hypoxia may alter the single-molecule arrangement and clustering of AT₁Rs. In this study, the AT₁R nanoscale distribution under control normoxic conditions in PC12 cells was determined using direct stochastic optical reconstruction microscopy (dSTORM). AT₁Rs were arranged in distinct clusters with measurable parameters. Across the entire cell surface there averaged approximately 3 AT₁R clusters/μm² of cell membrane. Cluster area varied in size ranging from 1.1 × 10^-4 to 3.9 × 10^-2 μm². Twenty-four hours of exposure to hypoxia (1% O₂) altered clustering of AT₁Rs, with notable increases in the maximum cluster area, suggestive of an increase in supercluster formation. These observations could aid in understanding mechanisms underlying augmented Ang II sensitivity in O₂ sensitive cells in response to sustained hypoxia.