Rearrangements and Junctional Region Characteristics in South Indian Patients With T-Cell Acute Lymphoblastic Leukemia

Department of Medical Oncology, Cancer Institute (WIA), Adyar, Chennai, Tamil Nadu, IndiaClonal T-cell receptor (TCR) gamma and delta gene rearrangements were studied in 40 T-ALLcases (pediatrics, 29; adults, 11) using PCR with homo-heteroduplex analysis. At least oneclonal TCRG or TCRD rearrangement was detected in 34 (85%) cases. TCR gamma (TCRG)rearrangement was detected in 25 (62.5%) cases that included 16 (55%) pediatrics and 9(81.8%) adults. TCR delta (TCRD) rearrangement was detected in 14/40 (35%) cases, whichincluded 12 (41%) pediatrics and 2 (18%) adults. The frequency of VgI-Jg1.3/2.3 was signifi-cantly more in adults than pediatrics (81.8% vs. 41.3%, P = 0.02). In TCRD,Vd1-Jd1 was rear-ranged in 10 (25%) cases. The surface membrane CD3 positive cases are significantly asso-ciated with absence of TCRD rearrangements (surface membrane CD3+ TCRd– 84% vs. sur-face membrane CD3– TCRd– 48%, P value = 0.03). Junctional region sequence analyzed with10 cases each, of TCRG and TCRD, revealed an average junctional region of 7.4 nucleotides(range 2–18 nucleotides) in TCRG and 27 nucleotides (range 14–42 nucleotides) in TCRD-complete rearrangements. In TCRG, trimming at the ends of Vg and Jg germline nucleotidesresulted in deletion, on an average of 9.2 nucleotides. In TCRD, deletion of nucleotides ofthe Vd and Jd gene segments on an average was 3.5 nucleotides. The junctional region ofTCRD is more diverse than TCRG; nevertheless, the frequency of TCRG was more than thatof TCRD and hence we rely more on TCRG clonal markers to quantitate the minimal residualdisease in T-ALL. Am. J. Hematol. 82:215–221, 2007.