CD14-CD15+, Possible Cells Are Potent Myeloid-Derived Suppressor Cells, Which Affect the Pathogenesis of Induction and Regression in Methotrexate-Mediated Lymphoproliferative Disorders

【Background】Despite numerous attempts to elucidate the mechanism underlying other iatrogenic immunodeficiency-associated lymphoproliferative diseases (OIIA-LPDs), the mechanism remains poorly understood. Methotrexate-associated lymphoproliferative disorder (MTX-LPD) is one of the disease entities included in OIIA-LPDs, which is especially developed in rheumatoid arthritis (RA) as we demonstrated (Tokuhira et al, Leuk Lymphoma. 2012;53:616-23). Spontaneous regression of LPD after MTX withdrawal is one of the distinct characteristics of MTX-LPD, and recent articles suggest that the increase in peripheral blood (PB) lymphocytes affect this phenomenon. However, the population of lymphocytes necessary to induce MTX-LPD regression is still unknown.

【Methods】We prospectively analyzed 10 patients with RA developing confirmed LPD during MTX administration, in our institutions between January 2014 to October 2015. All patients ceased MTX after developing lymphoadenopathies. To investigate the factors involved in spontaneous regression of LPD following MTX withdrawal, we performed flowcytometric analysis of whole blood including lymphocytes from PB for CD3, 4, 8, 14, 15, 20, 56, 127, and 45RO, HLA-DR, CCR3, CCR4, CCR6, CCR7, and EBV-tetramer expression, for all patients at three time points during the clinical course of treatment; at the time of MTX cessation (w0), and 4 weeks (w4) and 12 weeks (w12) after MTX cessation. We selected 10 age-, sex-, MTX dose-, and RA duration-matched RA patients treated with MTX for more than 6 months as controls, randomly selected from among the RA patients at our institutions. The patients with MTX-LPD were divided into two groups based on the status of LPD after MTX cessation, regressive LPD (R group) and persistent LPD (P group), and clinical parameters were compared.

【Results】In the 10 RA patients with MTX-LPD, the median age was 62.4 years (40-74), and the ratio of male:female patients was 2:8. The median duration from the time of RA diagnosis to the time of MTX development was 7.2 years (1.2-20.4), and the median duration of MTX administration was 4.3 years (0.7-9.8). The pathological diagnosis of LPDs was diffuse large B cell lymphoma (DLBCL, n=5), Classical Hodgkin lymphoma (cHL, n = 3), and non-specific LPD (LPD-nos, n=2). The averages values for LDH, CRP, and sIL-2R in the serum were 220 IU/mL (176-554), 0.85 mg/dL (0.06-2.53), and 579 IU/L(206-1210), respectively. The number of patients in the R group and the P group was 7 and 3, respectively. According to LPD phenotypes, all 5 cases of DLBCL belonged to the R group, whereas 1 of 3 HL and 1 of 2 LPD-nos belonged to the R group.

At w0, the median WBC count and absolute lymphocyte number in 10 MTX-LPD patients were 5810/µL (2700-11400) and 964/µL (220-2070), respectively. On the other hand, the median WBC count and absolute lymphocyte number in the 10 control patients were 5930/µL (3900-9000) and 1512/µL (755-2379), respectively. The absolute lymphocyte count in the P group was significantly higher than that in the R group. In addition, a significant increase in the lymphocyte number following MTX withdrawal was observed only in the R group, but not in the P group.

There were several observations from the flowcytometric analysis. First, the proportions of effector memory CD8+ T cells (EM CD8+), EBV specific CD8+ T cells, and T helper 1 (Th1) cells were significantly decreased both in the R group and in the P group compared to the control group at w0, and this subset was significantly increased in the R group at w4 and w12 compared to the P group. Second, the proportion of CD14-CD15+ cells in the lymphocyte fraction, which includes myeloid-derived suppressor cells (MDSC), was significantly increased in LPD group at w0, and significantly decreased following MTX cessation only in the R group, but not in the P group. Third, the proportion of CD14-CD15+ cells negatively and significantly correlated with the proportion of EM CD8+T cells (r2 = 0.47, p < 0.0001).

【Conclusions】Although the mechanism of MTX-LPD regression following MTX withdrawal is still unknown, this study demonstrates that reconstitution with specific lymphocytes in the PB is definitely correlated with LPD-regression. The proportion of Th1 cells, EM CD 8+, EBV specific CD8+ along with CD14-CD15+ cells dramatically indicated restoration and transition following MTX cessation, suggesting their potent effect toward the progression and regression of MTX-LPD.