Abstract 5741: Harnessing macrophages, while protecting T cells, enhances anti-tumor efficacy

Chimeric antigen receptor T (CAR T) cells are synthetically engineered to target specific tumor antigens. CD47 is a ubiquitous receptor that serves as a “don’t eat me” signal by binding to SIRPɑ on macrophages and is often over-expressed by cancer cells. Despite individual promise of CAR T and anti-CD47 therapies, neither has demonstrated clear efficacy in treating solid tumors in the clinic and there is thus an urgent need to develop novel approaches that enhance the potency of these therapies. We interrogated the potential pairing of CAR T with anti-CD47 therapy to overcome tumor resistance mechanisms inherent to each therapy alone, by engaging non-redundant properties of two arms of the immune system. However, upon coadministration of anti-CD47 therapy and CAR T cells across multiple tumor models in vivo, we observed potent and consistent macrophage-mediated clearance of CAR-T cells via on-target, off-tumor binding of anti-CD47 therapies to CAR T cells. This anti-CD47 mediated CAR T cell depletion blunts the therapeutic benefits of treatment and renders the pairing of the current versions of the two agents impractical.To overcome this challenge, we used directed evolution and yeast surface display to engineer a novel variant of CD47 (eCD47) with selective binding, identifying mutations that resulted in loss of binding to the anti-CD47 antibody B6H12, while maintaining the CD47 “don’t eat me” function through binding to SIRPɑ, which is essential for T cell persistence in vivo. T cells engineered to express eCD47, but not native, wild-type CD47, were resistant to targeting by multiple anti-CD47 antibodies but maintained binding to SIRPɑ. These T cells were no longer susceptible to anti-CD47 mediated macrophage phagocytosis in vitro, nor were they depleted in vivo after B6H12 administration. We demonstrated a striking improvement in therapeutic efficacy upon treatment of multiple solid tumor models when anti-CD47 therapy was combined with CAR T cells expressing eCD47, compared to combination with CAR T cells expressing wild-type CD47. We interrogated a mechanistic basis for this improved efficacy in an osteosarcoma model through single-cell RNA-sequencing of isolated tumors. We discovered that CAR T treatment led to a large influx of unique populations of macrophages into the tumor, which were lost upon CAR T depletion after anti-CD47 treatment. These T cell recruited-macrophages were maintained after anti-CD47 treatment in the presence of CAR T cells expressing eCD47, harnessing macrophage mediated anti-tumor activity after combination treatment. Thus, for the first time, eCD47 allows for effective pairing of CAR T therapy and anti-CD47 therapy for cancer treatment, by sparing T cells from macrophage mediated depletion, and revealing impressive synergy when adoptive T cell therapy is combined with macrophage activation.

Citation Format: Sean A. Yamada-Hunter, Johanna Theruvath, Molly T. Radosevich, Brianna J. McIntosh, Katherine A. Freitas, Naiara Martinez-Velez, Elena Sotillo, Amaury Leruste, Peng Xu, Moksha H. Desai, Bita Sahaf, Allison Banuelos, Savannah L. Wasserman, Irving L. Weissman, Jennifer R. Cochran, Crystal L. Mackall. Harnessing macrophages, while protecting T cells, enhances anti-tumor efficacy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5741.

The olfactory responses of the antenna and maxillary palp of the fleshfly, Neobellieria bullata (Diptera: Sarcophagidae), and their sensitivity to blockage of nitric oxide synthase

The relative sensitivities of the olfactory receptors in the antenna and maxillary palp of the fleshfly, Neobellieria bullata, were assessed using simultaneous electroantennograms (EAGs) and electropalpograms (EPGs). In general, the antennae and maxillary palps were more sensitive to odors related to animals (blood extract and saturated carboxylic acid) than to odors that were plant-derived (citral, hexenol, hexenal). In addition, the maxillary palps were relatively less sensitive to plant-derived odorants than the antennae, perhaps related to their anatomical position. Scanning electron microscopy was also used to assess the types of sensilla found on the two organs. In addition, NADPH-diaphorase histochemistry was used in an attempt to localize the enzyme nitric oxide synthase (NOS) in the antenna and the maxillary palps. We found evidence of NADPH-diaphorase staining in both organs, with localized staining in the antennal cells and more general staining in the maxillary palps. When NOS was selectively blocked using the antagonist L-NAME, the amplitude of the EAGs and EPGs to odorants fell by 30-50%. In contrast, application of the inactive enantiomer, D-NAME, did not change the amplitude of the EAGs or the EPGs. Our results indicate that NOS is involved in the function of olfactory receptor cells in the fleshfly.

Investigation of an occupational cancer cluster using a population-based tumor registry and the National Death Index

Occupational physicians investigate perceived cancer clusters to alleviate employee concerns and pursue etiologic hypotheses. We conducted a retrospective cohort analysis of all past and present employees of a metal fabrication plant and a comparison plant after employees recognized five cancer cases in 1987. We ascertained cases of all subjects who were employed at some time in the 8 years before 1987 through the Colorado Central Cancer Registry and determined vital status through the National Death Index. Cancer incidence at the index plant was almost identical to that of the population of the Denver metropolitan area (standardized incidence ratio [SIR] = 99, 95% confidence interval [CI] 59-165). Proportional incidence ratios revealed that no type of cancer occurred with significant excess in the index plant population during 1979 through 1986. Where population-based tumor registries exist, occupational physicians can employ this inexpensive and robust methodology to assess cancer incidence in exposed cohorts, pursue exposure-response relations, and evaluate clusters.

Labeling of Rh antibodies on solid-phase protein A

Rh0(D) antibodies which retain immune specificity after radiolabeling were prepared by a procedure which does not require IgG isolation from serum, requires 10-fold less isotope than conventional techniques and yields antibody solutions of defined composition. The method involves radioiodination of IgG on immobilized protein A, depends on employing human red cells reduced in surface cytophilic IgG, and exploits the inability of goat IgG to interact with Staphylococcus aureus protein A. The technique concentrates IgG by affinity adsorption and should prove useful in preparing radiolabeled alloantibodies from dilute human antisera and for red cell autoantibodies.