PROGRESSIVE REDUCTION OF CIRCULATING B LYMPHOCYTES IN PATIENTS WITH X-LINKED LYMPHOPROLIFERATIVE DISEASE (XLP)

BARÉ PATRICIA; PARODI CECILIA; MALBRÁN ALEJANDRO; E DE BRACCO M MARTA

BRITISH JOURNAL OF HAEMATOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016

0007-1048

Inactivating mutations of the SAP/SH2D1A/DSHP gene (Nichols et al, 1998) determine the occurrence of human X-linked lymphoproliferative disease (XLP), a condition associated to inappropriate response to Epstein-Barr virus (EBV) infection. XLP patients who survive fulminant infectious mononucleosis and hemophagocytic syndrome, causing 50 % death after initial EBV infection, may develop dysgammaglobulinemia or hypogammaglobulinemia and/or lymphoproliferative diseases. Inefficient immune response against EBV is unable to control EBV expansion in most cases. Abnormalities in the balance of T helper 1 (Th1)/ Th2 responses and accumulation of activated CD8+ T lymphocytes have been described (Czar et al, 2001; Belmonte et al, 2007). Concerning B lymphocytes, the percentage of memory B cells (CD27+ B lymphocytes) is reduced in XLP patients surviving primary EBV infection compared to that of normal controls (N) (Malbran et al, 2001). However, somatically mutated IgM+CD27+, but not Ig-subtype switched B cells could be found in XLP despite the absence of germinal centers in secondary lymphoid organs (Coraglia et al, 2010). Likewise, after prolonged culture of peripheral blood mononuclear cells (PBMC), the percentage of residual surviving B lymphocytes having a non-switched memory phenotype (IgM+IgD+CD27+) was higher than N in XLP patients (Belmonte et al, 2009). We have studied the long term (>10 years) evolution of the EBV viral load (EBV VL) and B lymphocyte profile in two surviving hypogammaglobulinemic siblings of an established XLP family (Malbran et al, 2001). One of them (#9) suffered EBV infection at adult age, developed severe EBV-associated disease and was treated with antiviral therapy and with Rituximab (Milone et al, 2005). He recovered from primary EBV infection, became hypogammaglobulinemic and received substitutive monthly intravenous immunoglobulins (IVIg) infusions until 2013, when he presented a bone marrow aplasia and was successfully allotransplanted. The older sibling (#4) developed XLP-related hypogammaglobulinemia after a tonsilar lymphoma at age 4, and remained on gamma globulin treatment for 35 years. Along this time, both patients were periodically evaluated searching for phenotypic and functional changes of both T and B lymphocytes. A predominant terminal effector memory CD8+ T cell phenotype (CD27-CD28-CD8+) was observed in patient #9 when compared to his brother (#4) (Belmonte et al, 2007). In this communication we report the progressive loss of B lymphocytes observed in both patients along the period of study, in coincidence with reduction of the EBV VL. While both patients shared the same genetic defect, their initial encounter with EBV occurred at different ages (childhood in #4 and at adult age #9) and they were treated differently. Patient #9 was 27 years old and had been asymptomatic before his XLP-marker disease (severe acute EBV infection). He had received preventive IgG replacement since he was genetically diagnosed as XLP. His EBV VL was 18164 EBV copies/106 leukocytes during the acute phase of his disease. At this time he received rituximab treatment and his CD19+ lymphocytes fell to < 0.5 %, coincident with a reduction of the EBV VL to 278. Two years after (Fig 1), the CD19 values started to increase, reaching the normal range six years after rituximab treatment. The EBV VL was still high two years after the acute phase of his disease (8620-8750 EBV copies/106 leukocytes) and persisted until year five (3969 EBV copies/106 leukocytes), becoming undetectable after six years (Fig 1). Patient #9 has never had any of the clinical symptoms of chronic active Epstein-Barr virus disease (Cohen et al, 2015). His B lymphocyte values steadily decreased, reaching 3.3-3.4 % with negative EBV VL seven years after his initial EBV-disease. This patient?s clinical condition required an allogeneic bone marrow transplant. This procedure was successfully done in the USA and he recovered his good health. We had no access to study the characteristics of his T and B lymphocytes, since he moved out of Argentina.Patient #4, who had his first XLP related condition at age 2, had low circulating CD19+ cells when we first studied his B lymphocyte profile (2-3 %, 33 years after his XLP-marker disease) (Fig 1). These values decreased further, reaching 0.34 % after 12 years of follow up, when he was 45 years of age. Along this period he continued receiving substitutive monthly IVIg, and his EBV VL remained below 100 EBV copies/106 leukocytes. As reported before (Malbran et al, 2001), memory CD27+ B lymphocytes were lower than normal in XLP. In both patients this value was relatively stable within the B lymphocyte pool oscillating around 5-14 % of the total B lymphocytes (Fig 1), but when the B lymphocyte percentages fell below 3 % in patient #4, memory B lymphocytes decreased to 0.5 %. In both patients the absolute B and CD4+ T lymphocyte values were lower (21-95 B lymphocytes/mm3; 1.60-11.3 memory B lymphocytes/mm3; 320-500 CD4+ T lymphocytes/mm3) compared to those of normal controls (72-200 B lymphocytes/mm3; 28-43 memory B lymphocytes/mm3; 600-900 CD4+ T lymphocytes/mm3), while CD8+ T lymphocytes were increased (700-3000 CD8+ T lymphocytes/mm3 in XLP and 320-700 CD8+ T lymphocytes/mm3 in N).It is difficult to explain why B lymphocytes were progressively reduced in these XLP patients. Several factors must be taken into account. It is known that germinal center persistence and formation are affected in XLP patients probably because TFH-B contacts are transient in the absence of SAP (Qi et al, 2008). This may lead to impaired B cell memory formation (Malbran et al, 2001; Coraglia et al, 2010). Continuous IgG replacement along many years may alter the balance of circulating B cells and their function. Inhibition of BCR-dependent and BCR-independent antigen presentation by B lymphocytes after IVIg infusion was demonstrated (Paquin Proulx et al, 2010). Also, CD8+ T lymphocytes reacting against EBV infected B lymphocytes could contribute to reduce the B cell count along many years.Replacement treatment with IgG will still be mandatory for the protection of these patients if they do not undergo allogeneic transplantation and recover the balance of their immune system. Anyway, progressive loss of B lymphocytes after many years of XLP evolution must be taken into account as an additional complication of this genetic defect.