Factors Affecting Natural Killer Cell Recovery after Autologous Stem Cell Transplantation in Multiple Myeloma
Authors: Keruakous Amany R. , Aljumaily Raid , Zhao Daniel , Asch Adam S. , Yuen Carrie 
Published: November 2021

Abstract
Introduction:
Natural killer (NK) cells are large granular lymphocytes, very potent effector lymphocytes that can induce cytotoxicity against a vast array of tumors without the need for antigen sensitization or antigen presentation by MHC class I. NK cells are believed to play important role in immune surveillance for cancer, limiting neoplastic progression, and effectors of anti-tumor therapies -by introducing Abs that block NK cell inhibitory receptors yielding improved NK cell-mediated lysis-
Retrospective studies demonstrated a significant correlation of NK cell recovery after autologous stem cell transplantation (ASCT) in multiple myeloma (MM) and disease outcomes. Higher absolute NK cell count one month after ASCT is associated with longer progression-free survival (PFS) and decreased risk of relapse. We aimed at investigating factors affecting NK cell recovery after ASCT in patients with multiple myeloma.
Method:
We designed a prospective cohort study, evaluating the potential factors that could affect NK cell recovery after ASCT. We included participants undergoing frontline ASCT for MM. We excluded participants with non-secretory myeloma or other malignancies that require active treatment, or with autoimmune disorders.
All participants received conditioning regimen consisted of melphalan 200 mg/m2 on day -2. In patients older than 65 years old given 100mg/m2 for 2 days. Dose reduction to 140 mg/m2 for patients with serum creatinine &gt; 2.0 mg/dL. Hematopoietic growth factor (peg-filgrastim 6 mg once subcutaneously) was given on day +1.
Absolute NK cell count (CD3-, CD56+ cells) was determined using flow cytometric immunophenotyping of peripheral blood two-three months after ASCT. To determine variables that affected NK cell recovery after ASCT, absolute NK cell count was dichotomized to less than the lower limit of normal "NK &lt; 76" and normal "NK &gt; or equal 76" following institutional normal reference range which is consistent with ARUP NK cell enumeration reference. Statistical analysis was performed using Fisher-Exact test for categorical variable and Wilcoxon rank test for continuous variables.
Results:
We analyzed the results of fifteen patients treated with frontline ASCT for multiple myeloma. With a median age at diagnosis of 60 years, ranging from 47 - 70 years. Of which 53 percent females and 47 percent males. Patients' baseline characteristics are described in Table 1
Our data showed that 63 percent of patients with post-transplantation ALC &gt; 1000 (5 of 8 patients), and 73 percent for ALC &gt; 500, (8 of 11 patients), had normal absolute NK cell count; with a correlation coefficient of 0.3 (Pearson Correlation Coefficients), suggesting a moderate linear correlation between absolute NK cell count and ALC two-three months after ASCT.
Patients' gender, age at ASCT, and comorbidity index (SORROR score) did not differ between the two groups of patients, P-value= 0.6193, 0.8454, 0.1721, respectively. Additionally, disease burden at the time of diagnosis, presence of CRAB criteria, involved free light chain and monoclonal immunoglobulins; all did not differ between the two cohorts. (Table 2)
Medications received before ASCT did affect the absolute NK cell count with a higher proportion of normal absolute NK cell count, and higher mean absolute NK cell in the cohort received double-class (PI plus IMiDs) when compared to triple-class (PI plus IMiDs plus Anti-CD 38 mAb) therapy before transplantation (mean NK cell count 125 and 53 Cell/μL, respectively), with marginal statistical significance P-value= 0.0667 (Fisher's Exact Test).
Discussion:
Our study showed that the addition of anti-CD38 mAb to myeloma induction regimen, associated with compromised NK cell recovery. Casneuf et al reported similar findings, in daratumumab-treated myeloma patients, total and activated NK-cell counts reduced rapidly in peripheral blood after the first dose, remained low throughout treatment, and recovered after treatment ended. Similar reductions were observed in the bone marrow.
Conclusion:
Medications received before transplantation potentially affect NK cell recovery in multiple myeloma patients. Although, the addition of anti-CD38 mAb to the myeloma induction regimen is associated with deeper response, its impact on immune reconstitution needs to be investigated on a larger sample size.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.