Lymphoma Cell Apoptosis in the Liver Induced by Distant Murine Cytomegalovirus Infection

Abstract

Cytomegalovirus (CMV) poses a threat to the therapy of hematopoietic malignancies by hematopoietic stem cell transplantation, but efficient reconstitution of antiviral immunity prevents CMV organ disease. Tumor relapse originating from a minimal residual leukemia poses another threat. Although a combination of risk factors was supposed to enhance the incidence and severity of transplantation-associated disease, a murine model of a liver-adapted B-cell lymphoma has previously shown a survival benefit and tumor growth inhibition by nonlethal subcutaneous infection with murine CMV. Here we have investigated the underlying antitumoral mechanism. Virus replication proved to be required, since inactivated virions or the highly attenuated enhancerless mutant mCMV-⌬MIEenh did not impact the lymphoma in the liver. Surprisingly, the dissemination-deficient mutant mCMV-⌬M36 inhibited tumor growth, even though this virus fails to infect the liver. On the other hand, various strains of herpes simplex viruses consistently failed to control the lymphoma, even though they infect the liver. A quantitative analysis of the tumor growth kinetics identified a transient tumor remission by apoptosis as the antitumoral effector mechanism. Tumor cell colonies with cells surviving the CMV-induced "apoptotic crisis" lead to tumor relapse even in the presence of full-blown tissue infection. Serial transfer of surviving tumor cells did not indicate a selection of apoptosis-resistant genetic variants. NK cell activity of CD49b-expressing cells failed to control the lymphoma upon adoptive transfer. We propose the existence of an innate antitumoral mechanism that is triggered by CMV infection and involves an apoptotic signal effective at a distant site of tumor growth.Complications of bone marrow transplantation (BMT) or hematopoietic stem cell transplantation include graft failure and graft-versus-host disease (46), infections, and minimal residual disease/leukemia giving rise to relapse of the initial tumor against which the hematoablative therapy was administered (12,16,21). Among infections in the immunocompromised BMT/hematopoietic stem cell transplantation recipients, human cytomegalovirus (hCMV) infection remains the most frequent and most severe (for recent reviews, see references 9, 17, and 33), despite antiviral therapy and although efficient reconstitution of antiviral immunity, of CD8 T cells in particular, can prevent lethal CMV organ disease in mouse models and in patients (for recent reviews, see references 22 and 34). While a wealth of literature separately deals either with tumor relapse or with CMV in clinical and experimental settings, information on an interference between CMV and tumors is scarce, except for a proposed role of hCMV genes in cell transformation (20, 57), a conspicuous association between hCMV and malignant gliomas (19), and an enhancement of tumor cell invasiveness by modulating the expression of adhesion molecules NCAM/CD56 and ␣5␤1 integrin VLA-5 in persistently infected neuroblastoma cells (8, 63). Tumor...

Activation of hepatic natural killer cells and control of liver-adapted lymphoma in the murine model of cytomegalovirus infection

“…Needless to emphasize that the dose of tumor cells has an impact on both the lethality of the tumor and the survival beneWt conferred by the infection. At the low dose of 10 4 E12E cells, which is a closer correlate to the clinical situation of MRD/L (see Introduction), »50% of the recipients survived long term, and the 50% survival beneWt was >8 months [25].…”

“…We therefore extended the established BALB/c model of mCMV infection in the setting of syngeneic experimental HSCT by intravenous transfer of the liver-adapted clonal variant E12E of the BALB/c-derived B cell lymphoma A20 (Fig. 1) [24,25]. Unlike the parental A20 cells, which are highly immunogenic in immunocompetent BALB/c mice but cause a highly aggressive, disseminated and neuroinvasive lymphoma in immunocompromised BALB/c mice, clone E12E is less immunogenic but highly tumorigenic in the liver.…”

“…It is essential to note that E12E is not permissive for mCMV infection and does not even express the immediateearly protein IE1, as evidenced by the absence of intranuclear IE1 protein and resistance to lysis by an IE1-speciWc cytolytic CD8 T cell line [25], so that the trivial antitumoral mechanism of cytopathic infection of the tumor cells was excluded by virtue of experimental model design. In addition, pre-incubation of E12E with either infectious or UVinactivated mCMV did neither interfere with tumor cell growth in cell culture nor with in vivo tumorigenicity in the target-organ liver, which proved that signaling to tumor cells or occupation of tumor cell surface receptors by the A very basic question that we addressed Wrst was if E12E cells really transmigrate through the discontinuous sinusoidal endothelium to establish lymphoma colonies within liver parenchyma or, alternatively, grow within the sinusoidal space.…”

“…It was all the more surprising then to Wnd a survival beneWt of »6 months by a simultaneous intraplantar infection with a moderate dose of 10 5 PFU of mCMV ( Fig. 1) [25], which is a very signiWcant period in the life span of mice. Needless to emphasize that the dose of tumor cells has an impact on both the lethality of the tumor and the survival beneWt conferred by the infection.…”

“…This was concluded from the Wnding that a panel of -herpesviruses HSV-1 and HSV-2, representing strains of broadly diVerent pathogenicity, did not control the E12E lymphoma under otherwise identical experimental conditions. Notably, this included HSV-1 strains JES and KOS as well as HSV-2 strain ER ¡ , which disseminate to and productively infect the liver, the target organ of E12E ( [25], J.P., unpublished data). This indicated that destruction of the stromal bed for tumor cell homing by cytopathic infection of the liver cells is unlikely to be the mechanism of tumor control in this organ.…”