The Presence Of Normal B and T Lymphocytes In Bone Marrow At Diagnosis Predicts Overall and Event Free Survival In Childhood B- Lineage Acute Lymphoblastic Leukaemia

 The absolute lymphocyte count (ALC) in peripheral blood has been shown to be a prognostic indicator in both adult and paediatric leukaemia. (Hudson et al 2004, Rabin et al 2012)The ALC is far easier and cheaper to measure than minimal residual disease in both developed and developing countries ^[1]. It is not known which lymphocytes in peripheral blood are important in predicting outcome or the mechanism for this.

We aimed to investigate the presence and subtype of normal lymphocytes present in the bone marrow at diagnosis in patients with B lineage acute lymphoblastic leukaemia and correlate with clinical outcome. We collected retrospective patient data from 101 patients at Alder Hey Children’s hospital diagnosed with B lineage ALL between 2002 and 2008. We aimed to identify normal non-tumour B and T lymphocytes present at diagnosis in bone marrow and correlate their presence with event free(EFS) and overall survival(OS).

Patient data was collected from 101 patients’ records  (including clinical prognostic information cytogenetics and MRD status). All patients had at least 5 years follow up.  Diagnostic flow cytometry list mode data files were analysed using WinMDI 2.9 software to determine the tumour populations, and proportions of non-tumour lymphocytes using CD20 and CD7 monoclonal antibodies, which were included in the original diagnostic panel. Proportions of these normal cell populations were correlated with patient outcome. One patient was excluded from the normal B cell analysis due to a high CD20 tumour expression.

The analysis of CD7 lymphocytes is shown in figure 1. 

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We analysed CD7+ cells as a % of the non-leukaemia cells. Using a threshold of 29.1% those with high CD7 cell numbers OS was 96.8% below the threshold OS was 85.3% (p=0.0017).  Event free survival was 93.6%v 82.3% in those with high v low numbers (p=0.004) see figure 1.

The mean proportion of CD20+ cells was 3.86% (SD +/- 7.66)% in the alive patients (n=94) and 1.21 (SD +/-0.75)% in deceased patients (n=6). Using a threshold value of 2.4% the overall survival in those with high CD20 cell numbers was 100.00% v 89.65% in those with low numbers, (p-= 0.03).

Similarly a strong trend was observed with CD20 numbers and event-free survival in patients above or below 2.7%, EFS was 97.1% and 87.9% respectively p= 0.129.

With modern therapy fortunately most children survive their leukaemia.  However there is a group of patients that remain not possible to cure with current chemotherapy approaches.

We present that the presence of normal CD7+ and CD20+ lymphocytes in the bone marrow at diagnosis are strongly associated with overall and event free survival. The mechanism of this effect is not known. We postulate that within these cell populations, that we have identified, is a specific immune response to the individuals own leukaemia. If this is the case these normal lymphocytes could be harvested and used as a potential individualised therapy.

No relevant conflicts of interest to declare.