CMV and immunosuppression

A herpes virus isn't just for Christmas; you have it for life. This is particularly true for cytomegalo virus (CMV) which about 85% of us get during the course of a lifetime. In order to stop it causing an illness we produce a lot of T cells to keep it under control. In older people these CMV-specific T cells comprise a sizable proportion of all of our T cells. In CLL an even larger proportion of our T cells are specifically programmed to fight CMV. In the issue of Blood for October 21st 2010, Paul Moss and his group from Birmingham, UK, have looked in detail of the effects of this accumulation.

They studied the CMV-specific CD4+ T-cell response in 45 patients and 35 age matched control subjects and demonstrated that it was markedly expanded in the patient group, averaging 11% of the CD4+ pool compared with 4.7% in controls. The magnitude of the CMV-specific CD4+ immune response increased with disease stage and was particularly high in patients who received chemotherapy. Within this group, the CMV-specific response comprised over 46% of the CD4+ T-cell repertoire in some patients. Serial analysis revealed that CMV-specific immunity increased during treatment with chemotherapy and remained stable thereafter.

Perhaps more important was the fact that overall survival was reduced by nearly 4 years in CMV-seropositive patients, and although this did not reach statistical significance larger series of patients might confirm this finding and this would be a worry that ought to be remedied.

Many studies of T-cells in patients with CLL and have shown abnormalities in the numbers and phenotype of CD4 and CD8 T cells, including inversion of the normal CD4:8 ratio and the accumulation of terminally differentiated effector T cells with relative absence of naive precursors. It has been suggested that these abnormalities contribute to the immunosuppression of B-CLL which I have written about and indicate the presence of a tumor-specific CD4+ T-cell response, though I have always doubted that this is so.

Rather than being an anti-tumor response, the rise in T cells has been postulated as being an anti-CMV response. Initial infection with CMV is associated with a vigorous CMV-specific immune response, which typically comprises over 2% of the CD8+ T-cell repertoire. In states of immunosuppression this value is often increased and is felt to represent cellular response to subclinical viral reactivation occurring during the immunosuppression. It has been shown that the CMV-specific CD8+ T-cell response is similarly increased in patients with CLL and the phenotype of CMV-specific cells was that of late differentiated effector cells. Much less has been known about the activity of the CD4+ CMV-specific T-cell response in either healthy donors or in patient groups.

The CD3+ T-cell count was increased by over 2 fold in CLL patients compared with controls. Furthermore, CMV seropositivity was associated with an increased CD3+ cell count in both the patients CMV seropositive 2648/mL vs CMV seronegative 2225/mL (P = 0.042) and the control group CMV seropositive 1100/mL vs CMV seronegative 792/mL, (P = 0.02). The CD4+ T-cell count was also increased in CLL patients (1139/mL vs 1262/mL) in comparison to the control group (467/mL vs 566/mL) but although the counts were higher in CMV pos patients and controls this did not reach statistical significance. In the patient group, the mean CD8+ T-cell count in CMV-seropositive donors was 1460/mL compared with 1070/mL in the CMV-seronegative group (P = .019). In the control group, the corresponding values were 541/mL and 175/mL, respectively (P < .001).

It is of interest that patients with CLL had increased T-cell counts compared with the control group, irrespective of CMV serostatus. The reasons for this are unknown but could reflect an increased immune component against other infectious agents or a possibly a tumor-specific immune response.

The CMV-specific CD4+ T-cell response was found to be significantly increased in CLL patients whether measured by expression of either IFN, TNF, or IL-2. The absolute number of CMV-specific CD4+ T cells was increased 3.5 fold in CLL patients compared with the control group (83 900/mL vs 24 100/mL for IFN, 79 300/mL vs 26 900/mL for TNF; and 23 200/mL vs 7850/mL for IL-2).

A significant increase in the frequency of CMV-specific CD4+ T cells was seen in patients at Binet stages B and C compared with patients at stage A of the disease. The mean value in patients with advanced disease was 15.2% of the CD4+ pool compared with 8.2% in patients at stage A disease (P = .03).

The CMV-specific CD4+ T cells response was greater in patients who had been treated. Despite the potentially immune suppressive effects of chemotherapy, the mean number of CMV-specific CD4+ T cells was increased in treated patients at 138 000/mL, 116 000/mL, and 39 200/mL for IFN, TNF, and IL-2 responses, respectively, compared with 55 900/mL, 42 400/mL, and 6270/mL in untreated patients (P = .047, P = .045, and P = .015 respectively). In two patients treated with respectively chlorambucil and fludarabine, the CMV-specific CD4+ T cells rose with treatment and then remained stable for a period. Interestingly, the rate of this increase was dependent on the nature of the treatment, and the half-life of T-cell expansion was measured at 40 days during fludarabine treatment and 120 days during chlorambucil treatment. They were not able to detect CMV reactivation by PCR within these patients, which indicates that viral replication is effectively controlled in CLL patients undergoing chemotherapy with fludarabine or chlorambucil.

The CMV-specific CD4+ T cells showed an effector memory phenotype of CD45RO+CD27–CD28–CD57+ expression. They observed that 9.5% of CD4+ T cells showed a CD28–CD57+ phenotype in CMV-seropositive patients compared with <1% in the uninfected group
Compared to the CMV positive controls, there was reduced expression of the important costimulatory and survival molecules CD27 and CD28, as well as CD45RA and CCR7, which are observed on naive and/or central memory cells, respectively. In contrast, the expression of CD57 and CD45RO, both of which are expressed on late differentiated effector memory cells, was increased in CMV-seropositive patients. These findings show that although CMV modulates the CD4+ T-cell repertoire in healthy donors, these effects are much more marked in the CLL patient group, which reflects the great increase in the absolute CMV-specific CD4+ T-cell count.

Comparison of the clinical features of the CLL cohort in relation to CMV serostatus showed that major infectious episodes were more commonly observed within the CMV-seropositive cohort. Features such as an increase in memory or CD57+ T cells have been associated with clinical complications of CLL. Serious infections such as pneumonia and shingles were seen only in the CMV-seropositive patients, and as the relative usage of fludarabine was comparable in both groups, this might suggest that CMV infection increases the degree of immune suppression within patients. Those patients who were seronegative for CMV demonstrated an increased survival compared with CMV-seropositive patients, with a median survival estimated of 157 months compared with 112 months. However, although the hazard ratio was 0.67 (95% CI: 0.25 to 1.81), indicating an observed 33% reduction in the risk of death for CMV-seronegative patients, this effect did not reach statistical significance due to the small cohort size (P = .42).