Mechanisms of resistance against T-cell engaging bispecific antibodies in multiple myeloma: implications for novel treatment strategies.

Off-the-shelf T-cell-redirecting bispecific antibodies targeting BCMA, GPRC5D, and FcRH5 have high activity in multiple myeloma with a manageable toxicity profile. However, not all patients respond to bispecific antibodies and patients can develop bispecific antibody resistance after an initial response. Mechanisms that contribute to bispecific antibody resistance are multifactorial and include tumour-related factors, such as high tumour burden, expression of T-cell inhibitory ligands, and antigen loss. Resistance due to antigen escape can be prevented by simultaneously targeting two tumour-associated antigens with a trispecific antibody or a combination of two bispecific antibodies. There is also increasing evidence that primary resistance to bispecific antibodies is associated with impaired baseline T-cell function. Long-term exposure to bispecific antibodies with chronic T-cell stimulation further aggravates T-cell dysfunction, which could contribute to failure of disease control. Therapeutic interference with T-cell exhaustion by targeting inhibitory or costimulatory pathways could improve bispecific antibody-mediated antitumour activity. The immunosuppressive microenvironment also contributes to bispecific antibody resistance. CD38-targeting antibodies hold promise as combination partners for bispecific antibodies because of their potential to eliminate CD38 ⁺ immune suppressor cells. In conclusion, a better understanding of the mechanisms underlying the absence of disease response has provided novel insights to optimise T-cell activity and bispecific antibody efficacy in multiple myeloma.
Competing Interests: Declaration of interests NWCJvdD has received research support, paid to his institution, from Janssen Pharmaceuticals, AMGEN, Celgene, Novartis, Cellectis, and BMS and has been on advisory boards for Janssen Pharmaceuticals, AMGEN, Celgene, BMS, Sanofi, Takeda, Roche, Novartis, Bayer, Adaptive, Kite Pharma, Merck, Pfizer, AbbVie, and Servier. AC has received research support from Janssen Pharmaceuticals; has received honoraria for lectures from Antengene; and has been a consultant or advisor for AbbVie, Adaptive, Amgen, Antengene, Bristol Myers Squibb, Forus, Genentech–Roche, GlaxoSmithKline, Janssen Pharmaceuticals, Karyopharm Therapeutics, Millennium–Takeda, and Sanofi–Genzyme. MVM has been on advisory boards for Amgen, Bristol Myers Squibb–Celgene, GlaxoSmithKline, Janssen Cilag, Kite Pharma, Oncopeptides, Pfizer, Roche, Sanofi, and Stemline and is a speaker bureau member of Janssen Cilag.
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