On May 9, 2022 Enlivex Therapeutics Ltd. (Nasdaq: ENLV, the "Company"), a clinical-stage macrophage reprogramming immunotherapy company, reported the poster presentation of a substantial survival benefit of AllocetraTM combined with immune checkpoint inhibition in a preclinical mesothelioma study at the International Society of Cell and Gene Therapy Annual 2022 Meeting (Press release, Enlivex Therapeutics, MAY 9, 2022, View Source [SID1234613905]). The poster was titled, "Allocetra-OTS, an Early Apoptotic Cellular Therapy Synergize with Chimeric Antigen Receptor (CAR) T Cell Therapy or Immune Check Point Inhibitor Against Peritoneal Solid Tumor."

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Mesothelioma, Treatment Landscape, and Macrophage-Solid Tumor Dynamics

Mesothelioma is one of the deadliest solid cancers with few treatment options, all of which have limited efficacy. People who are most at risk to develop mesothelioma generally have had long-term exposure to asbestos (e.g., construction workers, pipe fitters, and shipyard workers). It takes many years for mesothelioma to develop; it can appear 30 years after asbestos exposure. Immune checkpoint inhibitors targeting CTLA4 and PD1 are FDA-approved as first-line treatments for patients with unresectable malignant pleural mesothelioma.

In mesothelioma and in some other solid cancers, tumor cells, as part of their defense mechanisms, facilitate the recruitment of macrophages which become "pro-tumor" tumor associated macrophages (TAMs) rather than "anti-tumor" macrophages. The TAMs typically form a physical layer on top of the solid tumor, and induce immunosuppression in the solid tumor microenvironment. This in-turn promotes tumor growth and metastasis and makes it very difficult for the immune system or any anti-cancer drug to efficiently attack the cancerous cells. Allocetra is a cell therapy in development that is targeted at these TAMs, and its proposed mechanism of action is to change the balance of macrophage populations to skew towards anti-tumor macrophages and away from pro-tumor macrophages.

The Mesothelioma Model

To test the potential effect of cell therapy-induced macrophage reprogramming on difficult-to-treat solid tumors, Enlivex ran preclinical studies in which five groups of mice were implanted with mesothelioma cancer cells. The difference between the groups was the treatment given, which started on day 12 after the cancer’s initial growth period.

Results from multiple studies strongly support the potential of AllocetraTM to assist in the process of macrophage reprogramming in the solid tumor microenvironment and significantly change survival outcomes. As expected, only 1/16 (6%) of the untreated mice remained alive at day 42 (that one last remaining mouse died on day 65), compared with up to 25% survival for the mice in the group that was treated with the anti-CTLA4 immune checkpoint inhibitor. Surprisingly, AllocetraTM as a stand-alone treatment provided comparable survival rates as anti-CTLA4 monotherapy, with a 28.5% survival rate and a delayed cancer growth rate observed. Notably, the synergistic effect of treating with both drugs resulted in up to 100% survival with complete disappearance of the cancer. The effect was correlated with the AllocetraTM treatment dose. A lower dose of AllocetraTM provided slightly lower survival and cancer complete remission rates (67% complete remission for the low-dose treatment vs. up to 100% for the higher dose). The following chart provides a visual guide to the progressions/regression of the mesothelioma cancer in the different groups, as recorded for study mesothelioma AB12 137:

Across multiple studies of the AB12 mesothelioma model, anti-CTLA4 therapy significantly improved survival duration from mean 34±9 to 44.9 ±20 days (p<0.05). Allocetra as a stand-alone therapy improved survival duration to 52.3 ±20 days (p<0.02). The synergistic effect of the combination therapy of anti-CTLA4 + AllocetraTM improved survival duration to 86.7±20 days (p<0.0001) with complete cancer remission in 60-100% of mice, depending on the dose administered.

Prof. Dror Mevorach, Chief Scientific Officer of Enlivex, stated: "This reproducible and statistically significant data strongly support Allocetra’s proposed therapeutic mechanism of action of reprogramming macrophages in solid tumors. We believe that, in contrast to CAR-T, CAR-NK and other anti-cancer cell therapies directed at tumor antigens, AllocetraTM restores macrophage homeostasis in the tumor environment via reprogramming of pro-tumor macrophages. This may ultimately allow immune checkpoint inhibitors to be exponentially more effective."

Oren Hershkovitz, Ph.D., CEO of Enlivex, added: "Based on these results, Enlivex is planning to initiate a series of clinical trials during 2022 that are designed to evaluate Allocetra in combination with FDA-approved immune checkpoint inhibitor therapies in patients with advanced-stage solid tumors. To date, we have infused AllocetraTM in dozens of hospitalized patients in fragile condition resulting from sepsis and COVID-19-related organ dysfunction. We believe that the proposed differentiated mechanism of action of AllocetraTM, together with the safety and tolerability it has demonstrated in these prior studies, as well as the encouraging efficacy results of our preclinical solid tumor models, highlight an intriguing opportunity for Enlivex to provide another layer of life-saving therapy for patients who have few available options."

ABOUT ALLOCETRA

Allocetra is being developed as a universal, off-the-shelf cell therapy designed to reprogram macrophages into their homeostatic state. Diseases such as solid cancers, sepsis, and many others reprogram macrophages out of their homeostatic state. These non-homeostatic macrophages contribute significantly to the severity of the respective diseases. By restoring macrophage homeostasis, Allocetra has the potential to provide a novel immunotherapeutic mechanism of action for life-threatening clinical indications that are defined as "unmet medical needs", as a stand-alone therapy or in combination with leading therapeutic agents.