Anti-mesothelin OTS CAR T cells show better in vivo activity than Gavo-Cel in mesothelin-expressing tumors

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Preclinical research indicates that anti-mesothelin chimeric antigen receptor T cells may be more effective than gavocabtagen autoleucel in mesothelin-expressing tumors.

In comparison to gavoabtagene autoleucel (gavo-cel; TC-210), use of a ready-to-use anti-mesothelin T cell receptor fusion construct (MH1 γδ allo TRuC) demonstrated persistence and prolonged effectiveness live against mesothelin-expressing tumors in mice, according to results presented at the 2022 AACR Annual Meeting.1

Additionally, MH1 γδ allo TRuC T cells gave similar results in in vitro activity vs gavo-cel and MH1 γδ allo TRuC induced T cells live efficacy against SUIT2 tumors with low mesothelin expression. Finally, MH1 γδ allo TRuC T cells created with Alpha Constant T cell receptor (TRAC) and B2M multiplexed knockout retained full potency.

The presence of the TRC-alpha and TRC-beta subunits on gavo-cel may increase the risk of patients developing graft versus host disease (GVHD). To reduce alpha and beta T cell alloreactivity and reduce the risk of GVHD, the TRAC locus was knocked out of MH1 γδ allo TRuC T cells.

MH1 γδ allo TRuC T cells are generated CRIPSR/CAS9 is used to target TRAC to eliminate TCR cell surface expression. The lentivirus is then used to transduce primary T cells with allo TRuC transgenes to reassemble a non-alloreactive TCR. Allo TRuC transgenes consist of a single domain antibody (MH1) fused to the gamma and delta constant domains of the TCR. In contrast, gavo-cel is created by adding a TRuC transgene composed of a single domain antibody (MH1) that is fused to the extracellular domain of CD epsilon. Since gavo-cel retains its endogenous TCR alpha and beta subunits, they can react against allogeneic HLA-I molecules and cause GVHD.

In this mouse model, grafts of 1 x 106 MSTO-mesothelin cells mixed with Matrigel were injected subcutaneously into the right flank of NSG mice at day -21. When the tumors have reached 250 mm3 to 350 mm3 on day 0, investigators administered 2 x 106 intravenous MH1 γδ allo TRuC T or gavo-cel. Tumors were measured every 3-4 days to compare the effectiveness of each CAR T-cell therapy.

In a negative control group, a SUIT2 graft was injected on days -10 to -8 before injection of MH1 γδ allo TRuC or gavo-cel T cells on day 0 to examine the live efficacy of the 2 therapies vs SUIT2 cells. Notably, MH1 γδ allo TRuC T cells were administered with or without an interluken-15 fusion protein in the negative control group to improve persistence.

On day 19 following the T-cell injections, investigators took tissue samples from the blood, spleen, and liver and analyzed the samples for T-cell expansion and proliferation.

MH1 γδ allo TRuC T cells demonstrated prolonged tumor clearance compared to gavo-cel, with tumor volume increasing more over time when treated with gavo-cel compared to MH1 γδ allo TRuC T cells by 4 donors out of 5.

Additionally, when measuring 9 mice, normalized human CD45+ count levels (cells/µL) in blood, spleen, and liver were higher with MH1 γδ allo TRuC T cells compared to gavo- cel. MH1 γδ allo TRuC T cells also demonstrated increased persistence in vivo, with higher normalized number (cells/µL) of MH1 γδ allo TRuC T cells measured compared to gavo-cel by VHH detection.

In the negative control group, 3 animals that received MH1 γδ allo TRuC T cells with the IL-15 fusion protein resisted tumor growth longer than with MH1 γδ allo TRuC T cells alone, and 1 animal maintained tumor clearance throughout the study. . The study authors noted that these observations should be repeated in other donors.

References

Donaghey J, Kwong C, Powell A, et al. Engineering ready-to-use anti-mesothelin T cell receptor (TRuC™) fusion construct T cells. Presented at: 2022 AACR Annual Meeting; April 8-13, 2022; New Orleans, Louisiana. Accessed April 10, 2022. Shows 4716.

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