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Summary IGHV mutational status and ZAP‐70 or CD38 expression correlate with clinical course in B‐cell chronic lymphocytic leukaemia (CLL). The three markers may be discordant in the single case and there is no consensus on their combined use in clinical practise. This multicenter study investigated this issue. Two‐hundred and sixty‐two Binet stage A patients were studied for the three markers. Sixty patients were profiled with HG‐U133A gene expression chips. Disease progression was determined by time from diagnosis to treatment (TTT). The probability of being treatment‐free at 3 years was significantly shorter in patients with unmutated IGHV genes (IGHVunmut 66% vs. 93%, chi square of log‐rank = 30, P < 0·0001), ZAP‐70 positive (ZAP‐70pos 73% vs. 96%, chi square of log‐rank = 8·2, P = 0·004) or CD38‐positive cells (CD38pos 68% vs. 91%, chi square of log‐rank = 21, P < 0·0001). Cox multivariate regression analysis showed that the three markers had an independent predictive value for TTT of similar power. A prognostic system based on presence of none (low‐risk), one (intermediate‐risk) or two or three (high‐risk) markers was generated. Based on such criteria, 56%, 23% and 21% of cases were clustered in low (HR = 1), intermediate [HR = 2·8, 95% confidence interval (CI) 2·4–5·8] and high‐risk group (HR = 8·0, 95% CI 3·9–16·2). Specific transcriptional patterns were significantly associated with risk groups.

The expression of CD38 by B cells chronic lymphocytic leukemia (B-CLL) was studied in 20 untreated patients. The cells expressed abundant CD38 (relative fluorescence intensity range, 6 to 15) in 6 cases (group I patients), whereas CD38 expression was low to absent (relative fluorescence intensity range, 0 to 3) in the remaining cases (group II patients). Exposure of the cells from group I patients to goat antihuman mu chain antibodies (Ga mu-ab) resulted in the elevation of intracellular free Ca2+ concentration([Ca2+]i) followed by apoptosis. In contrast, exposure of group II cells to Ga mu-ab was not followed by increased levels of [Ca2+]i, programmed cell death or cell proliferation. No differences in the expression of surface IgM were noted in the two groups of B-CLL cells. Normal peripheral blood B cells, which expressed low to absent CD38, were capable of mobilizing [Ca2+]i and of proliferating after exposure to Ga mu-ab. The collected data suggest that, although group I B-CLL cells were able to transduce the signals delivered by IgM crosslinking, this pathway was severely impaired in group II B-CLL cells. However, unlike that observed in normal circulating B cells, stimulation of group I cells with Ga mu-ab resulted in apoptosis rather than proliferation. CD38 did not appear to be directly involved in [Ca2+]i mobilization induced by Ga mu-ab in group I B-CLL cells because their exposure to anti-CD38 monoclonal antibodies failed to cause [Ca2+]i mobilization or to block the [Ca2+]i response induced by Ga mu-ab. These data indicate that CD38 expression identified a particular subset of B-CLL cells with defined functional properties, including the propensity to undergo apoptosis.

Summary We have previously reported that about 80% of acute myeloid leukaemia (AML) samples tested at diagnosis constitutively expressed cytotoxic T‐lymphocyte‐associated antigen‐4 (CTLA‐4). The present study compared CTLA‐4 expression and function of leukaemic cells from AML patients at diagnosis with those from AML patients resistant to conventional chemotherapy. We also explored the possibility of targeting CTLA‐4 for apoptosis induction in chemoresistant AML cells. AML cells either from untreated patients (n = 15) or in chemoresistant phase (n = 10) were analysed for CTLA‐4 protein and transcript expression by flow cytometry and reverse transcription‐polymerase chain reaction respectively. CTLA‐4 expression was similar in untreated and in chemoresistant samples and was not associated with patients’ clinical features. In chemoresistant AML cells, CTLA‐4 transduced an apoptotic signal on engagement with its recombinant ligands r‐CD80 and r‐CD86, which induced an average of 71% and 62% apoptotic cells, respectively, at highest concentration. Apoptosis was equally induced in untreated leukaemic cells accompanied by cleavage of procaspase‐8 and ‐3. Thus, this study provides the first evidence that killing of leukaemic cells from AML patients may be obtained by the engagement of CTLA‐4 with its ligands, opening the way to a novel potential therapeutic approach based on triggering the CTLA‐4 molecule to circumvent chemoresistance in AML.

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