Rituximab is frequently used in the setting of ABO-incompatible renal transplants, and highly sensitized patients. Its interference with B-cell flow cytometric crossmatch (B-FCXM) is well known. However, its effect on the T-cell flow cytometric crossmatch (T-FCXM) has not been described. We aimed to evaluate the effect of rituximab on the T-FCXM using non-pronase and pronase treated donor lymphocytes and compare results with the single antigen bead (SAB) assay. In this retrospective study, 28 patients on rituximab therapy were evaluated against 30 donors. Using non-pronase treated donor lymphocytes, all 30 FCXMs showed strong B-cell positivity {median (IQR) B-cell ratio: 184.65 (253.17)} which significantly reduced {1.0 (1.18); p < 0.00001} with pronase treatment. ‘T-cell tailing’ phenomenon was observed in 17/30 FCXMs in the non-pronase group as a ‘tail of T-cells’, indicating a rare sub-population. However, it disappeared in the pronase-treated group. SAB assay did not show donor-specific antibodies (DSA) in all 17 patients with ‘T-cell tailing’ phenomenon. Although, rituximab is described to impact only B-FCXM, we have consistently found ‘T-cell tailing’ in 57% of T-FCXMs, which clears with pronase treatment. The ‘T-cell tailing’ led to weak positive T-FCMX ratios due to increased MFI in the FL1 channel. However, the absence of DSA in all recipients reinforces the fact that this is a false positive finding and should not be misconstrued as a possible class I DSA. Structural homology of Fc receptors on activated T-cells to CD20 could be a possible explanation of the same and provide insight into a novel mechanism of action of rituximab.

利妥昔单抗经常用于与ABO不相容的肾移植和高度敏感的患者中。它对B细胞流式细胞仪交叉匹配（B-FCXM）的干扰是众所周知的。但是，其对T细胞流式细胞仪交叉匹配（T-FCXM）的影响尚未描述。我们旨在评估使用非链酶和链酶处理的供体淋巴细胞对利妥昔单抗对T-FCXM的作用，并将结果与​​单抗原珠（SAB）分析进行比较。在这项回顾性研究中，针对30位捐赠者评估了接受利妥昔单抗治疗的28例患者。使用未经链霉蛋白酶处理的供体淋巴细胞，所有30种FCXM均显示出强大的B细胞阳性{中位数（IQR）B细胞比率：184.65（253.17）}，这明显降低了{1.0（1.18）；p <0.00001}，并使用链霉蛋白酶治疗。在非pronase组中的17/30 FCXM中观察到“ T细胞拖尾”现象，称为“ T细胞尾巴”，表明罕见的亚群。然而，在链霉蛋白酶治疗组中它消失了。SAB分析未在所有17例具有“ T细胞拖尾”现象的患者中显示供体特异性抗体（DSA）。尽管据描述利妥昔单抗仅影响B-FCXM，但我们始终在57％的T-FCXM中发现“ T细胞拖尾”，可通过链霉蛋白酶处理清除。由于FL1通道中的MFI增加，“ T细胞拖尾”导致T-FCMX正比变弱。但是，在所有接受者中都没有DSA的事实进一步证明了这是一个错误的积极发现，不应将其误认为是可能的I类DSA。