[Analysis of T cell repertoire in children with acute B lymphoblastic leukemia]

The complementarity determining region 3 (CDR3) of T cell receptor (TCR) is the place through which T cells connect to the antigen. The lengths and DNA sequences of CDR3s are different according to different T cell clones. This leads to a diverse TCR CDR3 repertoires which can reflects the functional status of T cells precisely. This study aimed at elucidating the abnormality of TCR beta chain variable region (BV) CDR3 repertoires of children with acute B lymphoblastic leukemia, the pathogenesis of leukemia associated with T cell dysfunction and the immuno-reconstruction of T cells after the chemotherapy.

Twelve children aged from 3 to 13 years (average 4.50 +/- 3.78 years) with acute B lymphoblastic leukemia before chemotherapy and 8 healthy control donors aged from 6 to 16 years (average 10.30 +/- 3.00 years) were enrolled. Four of 12 patients were studied for the second time 3 months after complete remission (CR). Reverse transcription-polymerase chain reaction (RT-PCR) and polyacrylamide sequencing gel electrophoresis were used to detect the diversity of TCR BV CDR3 repertoires of these children.

(1) The expression of BV2 and BV3 in 12 children increased and BV17 and BV18 decreased before the chemotherapy as compared with controls (P < 0.05). There were 4 children with a lower level expression of BV21 before the chemotherapy, and much lower level expression was found after the remission. (2) Normally each lane contained eight to ten bands, which represented unique CDR3 sizes for a given TCR BV family. Bands differed in size by 3 nucleotides and generally form a Gaussian distribution. There were 14% TCR BV families with abnormal CDR3 length distribution in 12 patients before therapy, which was significantly higher than that of controls (5.5%, P < 0.05). Restricted CDR3 length distribution was observed in BV14, BV1, BV16, BV20, BV13.1, BV13.2 and BV6. Every abnormal BV family recovered to normal Gaussian distribution 3 months after CR.

T lymphocytes in children with acute B lymphoblastic leukemia revealed markedly skewed repertoires, which suggests the abnormality of T cell functions. Most abnormal T cell repertoires recovered to normal Gaussian distribution 3 months after the first CR, which suggests the immunological reconstitution of T cell repertoires.