CD4+ T cells contribute to tumor eradication, even in the absence of CD8+ T cells. Cytotoxic CD4+ T cells can directly kill MHC class II positive tumor cells. More surprisingly, CD4+ T cells can indirectly eliminate tumor cells that lack MHC class II expression. Here, we review the mechanisms of direct and indirect CD4+ T cell-mediated elimination of tumor cells. An emphasis is put on T cell receptor (TCR) transgenic models, where anti-tumor responses of naïve CD4+ T cells of defined specificity can be tracked. Some generalizations can tentatively be made. For both MHCIIPOS and MHCIINEG tumors, presentation of tumor specific antigen by host antigen presenting cells (APCs) appears to be required for CD4+ T cell priming. This has been extensively studied in a myeloma model (MOPC315), where host APCs in tumor-draining lymph nodes are primed with secreted tumor antigen. Upon antigen recognition, naïve CD4+ T cells differentiate into Th1 cells and migrate to the tumor. At the tumor site, the mechanisms for elimination of MHCIIPOS and MHCIINEG tumor cells differ. In a TCR transgenic B16 melanoma model, MHCIIPOS melanoma cells are directly killed by cytotoxic CD4+ T cells in a perforin/granzyme B-dependent manner. By contrast, MHCIINEG myeloma cells are killed by IFN-g stimulated M1-like macrophages. In summary, while the priming phase of CD4+ T cells appears similar for MHCIIPOS and MHCIINEG tumors, the killing mechanisms are different. Unresolved issues and directions for future research are addressed.

Primary plasma cell leukemia (PCL) has a consistently ominous prognosis, even after progress in the last decades. PCL deserves a prompt identification to start the most effective treatment for this ultra-high-risk disease. The aim of this position paper is to revisit the diagnosis of PCL according to the presence of circulating plasma cells in patients otherwise meeting diagnostic criteria of multiple myeloma. We could identify two retrospective series where the question about what number of circulating plasma cells in peripheral blood should be used for defining PCL. The presence of ≥5% circulating plasma cells in patients with MM had a similar adverse prognostic impact as the previously defined PCL. Therefore, PCL should be defined by the presence of 5% or more circulating plasma cells in peripheral blood smears in patients otherwise diagnosed with symptomatic multiple myeloma.

Venetoclax (Ven) is a selective small‐molecule inhibitor of BCL‐2 that exhibits antitumoral activity against MM cells with t(11;14) translocation. We evaluated the safety and efficacy of Ven and dexamethasone (VenDex) combination in patients with t(11;14) positive relapsed/refractory (R/R) multiple myeloma (MM). This open‐label, multicenter study had two distinct phases (phase one [P1], phase two [P2]). Patients in both phases received VenDex (oral Ven 800 mg/day + oral Dex 40 mg [20 mg for patients ≥75 years] on days 1, 8, and 15, per 21–day cycle). The primary objective of the P1 VenDex cohort was to assess safety and pharmacokinetics. Phase two further evaluated efficacy with objective response rate (ORR) and very good partial response or better. Correlative studies explored baseline BCL2 (BCL‐2) and BCL2L1 (BCL‐X_L) gene expression, cytogenetics, and recurrent somatic mutations in MM. Twenty and 31 patients in P1 and P2 with t(11;14) positive translocation received VenDex. P1/P2 patients had received a median of 3/5 lines of prior therapy, and 20%/87% were refractory to daratumumab. Predominant grade 3/4 hematological adverse events (AEs) with ≥10% occurrence included lymphopenia (20%/19%), neutropenia (15%/7%), thrombocytopenia (10%/10%), and anemia (5%/16%). At a median follow‐up of 12.3/9.2 months, ORR was 60%/48%. The duration of response estimate at 12 months was 50%/61%, and the median time to progression was 12.4/10.8 months. In biomarker evaluable patients, response to VenDex was independent of concurrent del(17p) or gain(1q) and mutations in key oncogenic signaling pathways, including MAPK and NF‐kB. VenDex demonstrated efficacy and manageable safety in heavily‐pre‐treated patients with t(11;14) R/R MM.

T-cell redirecting therapy (TCRT), specifically chimeric antigen receptor T-cell therapy (CAR T-cells) and bispecific T-cell engagers (TCEs) represent a remarkable advance in the treatment of multiple myeloma (MM). There are several products available around the world and several more in development targeting primarily B-cell maturation antigen (BCMA) and G protein–coupled receptor class C group 5 member D (GRPC5D). The relatively rapid availability of multiple immunotherapies brings the necessity to understand how a certain agent may affect the safety and efficacy of a subsequent immunotherapy so MM physicians and patients can aim at optimal sequential use of these therapies. The International Myeloma Working Group conveyed panel of experts to review patient and disease-related factors affecting efficacy and safety of immunotherapy, summarize existing information on sequencing therapy and provide a series of core recommendations.

In the post-pandemic COVID-19 period, human activities have returned to normal and COVID-19 cases are usually mild. However, patients with multiple myeloma (MM) present an increased risk for breakthrough infections and severe COVID-19 outcomes, including hospitalization and death. The European Myeloma Network has provided an expert consensus to guide patient management in this era. Vaccination with variant-specific booster vaccines, such as the bivalent vaccine for the ancestral Wuhan strain and the Omicron BA.4/5 strains, is essential as novel strains emerge and become dominant in the community. Boosters should be administered every 6–12 months after the last vaccine shot or documented COVID-19 infection (hybrid immunity). Booster shots seem to overcome the negative effect of anti-CD38 monoclonal antibodies on humoral responses; however, anti-BCMA treatment remains an adverse predictive factor for humoral immune response. Evaluation of the immune response after vaccination may identify a particularly vulnerable subset of patients who may need additional boosters, prophylactic therapies and prevention measures. Pre-exposure prophylaxis with tixagevimab/cilgavimab is not effective against the new dominant variants and thus is no longer recommended. Oral antivirals (nirmatrelvir/ritonavir and molnupiravir) and remdesivir are effective against Omicron subvariants BA.2.12.1, BA.4, BA.5, BQ.1.1 and/or XBB.1.5 and should be administered in MM patients at the time of a positive COVID-19 test or within 5 days post symptoms onset. Convalescent plasma seems to have low value in the post-pandemic era. Prevention measures during SARS-CoV-2 outbreaks, including mask wearing and avoiding crowded places, seem prudent to continue for MM patients.