FLT3-ITD and FLT3-TKD mutations were observed in approximately 20 and 10% of acute myeloid leukemia (AML) cases, respectively. FLT3 inhibitors such as midostaurin, gilteritinib and quizartinib show excellent response rates in patients with FLT3-mutated AML, but its duration of response may not be sufficient yet. The majority of cases gain secondary resistance either by on-target and off-target abnormalities. On-target mutations (i.e., FLT3-TKD) such as D835Y keep the TK domain in its active form, abrogating pharmacodynamics of type II FLT3 inhibitors (e.g., midostaurin and quizartinib). Second generation type I inhibitors such as gilteritinib are consistently active against FLT3-TKD as well as FLT3-ITD. However, a “gatekeeper” mutation F691L shows universal resistance to all currently available FLT3 inhibitors. Off-target abnormalities are consisted with a variety of somatic mutations such as NRAS, AXL and PIM1 that bypass or reinforce FLT3 signaling. Off-target mutations can occur just in the primary FLT3-mutated clone or be gained by the evolution of other clones. A small number of cases show primary resistance by an FL-dependent, FGF2-dependent, and stromal CYP3A4-mediated manner. To overcome these mechanisms, the development of novel agents such as covalently-coupling FLT3 inhibitor FF-10101 and the investigation of combination therapy with different class agents are now ongoing. Along with novel agents, gene sequencing may improve clinical approaches by detecting additional targetable mutations and determining individual patterns of clonal evolution.

Tumor cells use immune-checkpoint pathways to evade the host immune system and suppress immune cell function. These cells express programmed cell-death protein 1 ligand 1 (PD-L1)/PD-L2, which bind to the programmed cell-death protein 1 (PD-1) present on cytotoxic T cells, trigger inhibitory signaling, and reduce cytotoxicity and T-cell exhaustion. Immune-checkpoint blockade can inhibit this signal and may serve as an effective therapeutic strategy in patients with solid tumors. Several trials have been conducted on immune-checkpoint inhibitor therapy in patients with malignant lymphoma and their efficacy has been reported. For example, in Hodgkin lymphoma, immune-checkpoint blockade has resulted in response rates of 65% to 75%. However, in non-Hodgkin lymphoma, the response rate to immune-checkpoint blockade was lower. In this review, we evaluate the biology of immune-checkpoint inhibition and the current data on its efficacy in malignant lymphoma, and identify the cases in which the treatment was more effective.

We conducted a prospective, three-center, observational study in Japan to evaluate the prevalence of seropositivity and clinically protective titer after coronavirus disease 2019 vaccination in patients with plasma cell dyscrasia(PCD). Two-hundred sixty-nine patients with PCD [206 symptomatic multiple myeloma (MM)] were evaluated. Seropositivity was observed in 88.7% and a clinically protective titer in 38.3% of MM patients, both of which were significantly lower than those of healthy controls. Patients receiving anti-CD38 antibodies had much lower antibody titers, but antibody titers recovered in those who underwent a wash-out period before vaccine administration. Older age (≥65), anti-CD38 antibody administration, immunomodulatory drugs use, lymphopenia (<1000/μL), and lower polyclonal IgG (<550 mg/dL) had a negative impact for the sufficient antibody production according to multivariate analysis. Patients with clinically protective titer had a significantly higher number of CD19+ lymphocytes than those with lower antibody responses (114 vs. 35/μL, p = 0.016). Our results suggested that patients with PCD should be vaccinated, and that the ideal protocol is to temporarily interrupt anti-CD38 antibody therapy for a “wash-out” period of a few months, followed by a (booster) vaccine after the B-cells have recovery. Supplementary Information The online version contains supplementary material available at 10.1007/s12185-022-03300-4.

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Patients with lymphoma are at increased risk for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); therefore, evaluation of SARS-CoV-2 vaccination efficacy is essential. We conducted a prospective observational study to monitor the antibody response in 500 patients with lymphoma after SARS-CoV-2 vaccination. Antibody levels increased in a stepwise manner after the first and second dose of the vaccine. After completion of the two-dose series, anti-S antibody was negative in 109 patients (21.8%), and below clinically protective levels (anti-S ≥ 264 U/mL) in 236 patients (47.2%). The median anti-S titers at 0–6 months, 7–12 months, 13–24 months, and 24 months after treatment completion were 0.4 U/mL, 3.8 U/mL, 270 U/mL, and 650 U/mL, respectively. Multivariate analysis showed that receiving the vaccine < 6 months since completing treatment, white blood cell count < 5050/μL, percentage of CD19 + cells < 10%, CD4 + cells < 27%, immunoglobulin (Ig) A < 195 mg/dL, IgM < 50 mg/dL, serum soluble interleukin 2 receptor > 600 U/mL, and presence of lymphoma cells in the peripheral blood were significantly correlated with anti-S < 264 U/mL. Lymphoma patients had variably impaired antibody response to the SARS-CoV-2 vaccine. We identified various factors to predict COVID-19 vaccine effectiveness in lymphoma patients that may help tailoring possible vaccine boosters. Supplementary Information The online version contains supplementary material available at 10.1007/s12185-022-03305-z.

Summary This study reports the relationship between CD38+ regulatory T cells (Tregs) and messenger RNA coronavirus disease 2019 (mRNA‐COVID‐19) vaccination in 60 patients with plasma cell dyscrasia. Patients treated with anti‐CD38 monoclonal antibodies (mAbs) had significantly lower CD38+ Tregs than those not treated (0.9 vs. 13.2/μl). Late‐responders, whose antibody titres increased from weeks 4–12 after the second vaccination, had significantly lower CD38+ Treg counts than non‐late‐responders (2.5 vs. 10.3/μl). Antibody titres in patients with lower CD38+ Treg levels were maintained from weeks 4–12 but decreased in those with higher CD38+ Treg levels. Therefore, depletion of CD38+ Tregs by anti‐CD38 mAbs may induce a durable response to mRNA‐COVID‐19 vaccination.

Cr, creatinine; dFLC, difference between involved free light chain (FLC) and uninvolved FLC; eGFR, estimated glomerular filtration rate; iFLC, involved FLC; NA, not available; no., number.