Post-treatment loss of MMR vaccine immunity in multiple myeloma patients following autologous stem cell transplantation: A retrospective cohort analysis

Abstract

Abstract Background Multiple myeloma (MM), a clonal plasma cell malignancy, accounts for approximately 10% of all hematologic neoplasms. Patients with MM are particularly susceptible to infections, especially following high-intensity treatments such as autologous stem cell transplantation (ASCT) and chimeric antigen receptor (CAR) T-cell therapy. Although humoral immunity to measles, mumps, and rubella (MMR) might wane after such therapies, real-world data on post-treatment serologic immunity remains scarce. In light of recent measles outbreaks in the United States, this study aims to assess the prevalence of MMR immunity among MM patients following ASCT. Methods We conducted a retrospective descriptive analysis of multiple myeloma patients who underwent autologous stem cell transplantation (ASCT) as upfront consolidation, with at least 12 months post-ASCT. Measles, mumps, and rubella (MMR) IgG titers were assessed during routine follow-up and standardized: measles and mumps IgG <5 IU/mL were set to 0 and capped at 300 IU/mL; rubella <10 IU/mL was set to 0 with no upper limit applied. Serologic immunity was defined based on the following thresholds: measles ≥16.5 IU/mL, mumps ≥11 IU/mL, and rubella ≥10 IU/mL. Median antibody titers were reported overall and stratified by immune status. Patients who received IVIG within 8 weeks of titer measurement were excluded. Comparisons were made across clinical subgroups, including response status, receipt of maintenance therapy, and CMV status. Results A total of 131 patients evaluated in the myeloma clinic between March and July 2025 were included in the analysis. Overall, 24/98 (24.5% of patients) were non-immune to all three viruses and individually, 35.4% lacked immunity to measles, 33% to rubella, and 73.26% to mumps. Immune patients demonstrated higher median titers compared to non-immune for measles [120.5 (16.8 - 300) vs 0 (0-13.3) IU/mL, p < 0.001], rubella [26.6 (10–509) vs 0 (0–0) IU/mL, p < 0.001], and mumps [33.6 (12.7–300) vs 0 (0–10.4) IU/mL, p < 0.001]. Median time from ASCT to serologic testing was slightly longer in immune versus non-immune patients for measles (51 vs 49 months, p = 0.838) and rubella (51 vs 47 months, p = 0.365), with comparable timing for mumps (50 vs 50.5 months, p = 0.59). Among immune patients, VGPR group had higher immunity to measles (50% CR, 57.1% VGPR, 45.6% PR) and rubella (60.3% VGPR, 47.2% CR, 50% PR) while immunity to mumps remained consistently low across all groups (19.4% CR, 25.4% VGPR, 18.2% PR). Maintenance therapy was associated with lower, though non-significant, median titers for measles (41.5 vs 50 IU/mL), mumps (0 vs 4.2 IU/mL), and rubella (15.3 vs 28.2 IU/mL). CMV seropositivity correlated with a non-significant increase in measles titers, with no notable differences for mumps or rubella. Conclusion Protective serologic immunity to one or more MMR vaccination components is lacking in a significant number of MM patients post cellular therapy. These results emphasize how crucial routine post-treatment serologic surveillance is, and they could help guide revaccination plans to maximize infection protection in this population at risk.