Kinetics of humoral immunodeficiency with bispecific antibody therapy in multiple myeloma.
Authors: Hammons Lindsay , Szabo Aniko , Dhakal Binod , Venniyil Radhakrishnan Sabarinath , Chhabra Saurabh , D'Souza Anita , Mohan Meera 
Published: June 2022

8049 Background: Bispecific antibodies (bsAb) are a promising class of therapeutics in RRMM. While hypogammaglobinemia (HGG) is anticipated due to plasma cell depletion, there is a lack of information about the degree of secondary immunodeficiency and resultant infectious complications. We investigated the kinetics of HGG in patients with RRMM on bsAb therapy. Methods: We identified and followed 42 patients treated on early clinical trials of bsAb at our institution between 2019 and 2021. Serial immunoglobulin levels and infections were obtained from the start of therapy until last follow up or 3 months after study exit. Results: 49 treatment courses were included from 42 individual patients. All patients were triple class exposed with a median of 5 prior lines of therapy. The median age was 67 (44-85) years, with 49% females. African Americans accounted for 18% of patients. 96% of patients had at least one prior ASCT. 90% of patients received bsAb targeting BCMA including 7 patients who received more than one line of BCMA targeting therapies. At a median follow up 9.5 (0.9-28.6) months, 40.8% of patients remained on bsAb therapy. At the start of therapy, the median IgG, IgA, and IgM levels were 560 (44-9436), 15 (5-3886) and 6 (5-64) mg/dL, respectively and 50% of patients had severe HGG (≤400mg/dl). Serum IgG levels reached a nadir at 3 months while, IgA and IgM at 1 month, from the start of therapy. The median nadir levels of IgG were 159 (40-2996) mg/dL, while it was < 5 mg/dL for both IgA and IgM. IgG levels were below the detectable range ( < 40 mg/dl) in 28% of patients at some point during therapy. IgA and IgM were also below the detectable range ( < 5 mg/dl) in 50% and 60% of patients, respectively. At last follow-up, the median IgG levels were 444 (40-1860) mg/dL and IgA 5 (5-254) mg/dL and IgM 5 (5-44) mg/dL. Additionally, 38% of patients remained severely hypogammaglobinemic. 57% (24/42) of patients received IVIG supplements in the current series. About 71% of patients had at least one infectious event and the cumulative incidence of infections progressively increased with increasing duration of therapy with risk at 3, 6, 9 12, 15 months being 41%, 57%, 64%, 67% and 70%, respectively. Among these, 54% of infection were bacterial. Viral infection accounted for 41% of infections. A third of patients had new infectious events during the first 90 days following stopping bsAb treatment. 57% (8/14) of patients did not mount a response to the primary COVID19 immunization series. Among the five patients with repeat antibody titers after the booster dose, 50% were still not able to mount an antibody response. Conclusions: bsAb therapy in RRMM can be associated with profound and prolonged HGG. The cumulative risk of infection correlated with the degree of HGG and progressively increases with treatment and persisted months after being off therapy. Additionally, an impaired antibody response to the COVID-19 immunization series was also noted.