EBV-HLH suffers a poorer prognosis than other subtypes of secondary HLH, especially relapsed and refractory EBV-HLH [17,18]. Without effective treatment, short term mortality is high, and most patients with relapsed EBH-HLH die within first few weeks .Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is often required for EBV-HLH, especially for adults and refractory/relapsed patients. It is thought that allo-HSCT is possible to induce immune reconstitution, thus enabling patients to effectively eliminate EB virus[3,19]. In one Japanese cohort, allo-HSCT resulted in an 85.7% 10-year OS for patients with EBV-HLH . In a retrospective analysis from our center, 27.1% of patients with EBV-HLH received allo-HSCT, and the final survival rate was 52.78% . However, some patients in the actual situation are unable to perform allo-HCST due to various factors. It has been reported that granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blood stem cells (GPBSCs) infusion can mediate GVL effects and hasten hematologic recovery without amplifying GVHD in AML . Considering the important position of allo-HSCT, we tried to use GPBSCs infusion as a salvage treatment in patients with refractory EBV-HLH. This study found that for patients with refractory EBV-HLH, GPBSCs infusion therapy can more effectively reduce EBV-DNA levels after 2 weeks and 4 weeks, but has no significant effect on the recovery of blood picture. The 3-month survival was improved, but no significant effect on overall survival.
G\PBSCs infusion therapy in the treatment of leukemia reported in the previous literature can significantly shorten the recovery time of white blood cells and platelets . GPBSCs is a stimulated cell infusion. The current speculation is that, in contrast to unstimulated DLI, the larger number of lymphocytes, CD34 cells, natural killer (NK) cells, as well as cytokines, contained in G-PBSCs may contribute roles in promoting hematopoietic recovery.[13,22]. However, in this study, there was no significant difference in the recovery of blood picture in the GPBSCs infusion group compared with the uninfused group, although similar levels of donor chimerism were observed in this study, which was consistent with the previous study of leukemia. There may be possibility that the disease state of HLH is different from leukemia. The decline of the blood cells in HLH is mainly related to the production and action of a large number of inflammatory mediators . This is different from the bone marrow suppression caused by chemotherapy drugs in treatment of leukemia. HLH needs to be controlled by controlling inflammatory cells and then the controlling of inflammatory factor storm . However, the mechanism of hematopoietic recovery of GPBSCs is still unclear, especially when it’s in HLH, and the specific internal mechanism still needs further study.
Interestingly, the GPBSCs infusion after chemotherapy was more effective at reducing EBV-DNA viral load than the regular chemotherapy. This may be similar to the GVL effect of GPBSCs in the treatment of leukemia: the lymphocytes of the infused donor cells act synergistically with the recipient's immune system to delete EBV-infected cells, thereby reducing Epstein-Barr virus load. However, prior studies suggested that the main mediator of GVL in leukemia is NK cells, and other cells, such as T cells, mainly function GVL by interacting with the recipient's immune system [13,24]. However, in HLH, EB virus’ clearance mainly relies on EB virus-specific CD8 + T cells . Previous studies have found that EBV-specific CD8 + T recombination happens in the early phase of allo-PBSCT, even if the total number of T cells decreased, the proportion of CD8 + T still elevated, but this phenomenon was not observed in cord blood transplantation . The GVL effect of DLI is mainly through donor chimerism or mixed chimerism . In this study, only one patient achieved mixed chimerism after infusion of cells, although the number of cells infused is not different from other patients. This patient eventually died of GVHD, but the EBV viral load of this patient decreased significantly, and EBV-DNA turned negative after 4 weeks. This suggests that the effect of the reduction of EBV-DNA is achieved by the GVL-like effect of lymphocytes in the infused cells, just like in leukemia. With the patients who tested chimerism in this study, all of them were microchimerism except the patient mentioned above. Almost all patients with microchimerism did not develop mixed chimerism suggesting that GPBSCs is difficult to achieve donor chimerism or mixed chimerism. However, with the persistence of micro-chimerism, a small number of donor cells persist in the patient, this micro-chimerism may be the main reason for GPBSCs to effectively reduce EBV-DNA level. Due to the small sample size of this study, the correlation between the micro-chimerism rate and the EBV-DNA levels decline was not found. However, in the previous micro-transplant study, the micro-chimerism rate reached a peak at 7d-14d after infusion . This is consistent with the efficacy of EBV-DNA’s reduction was maximally in 2 weeks, but more data was needed to validate the relationship. However, the efficacy of EBV-DNA reduction cannot persist as in 4 weeks after treatment, there’s no differences of EBV-DNA level between 2 groups. We speculate that the loss of differences in EBV viral load are related to possible depletion of GPBSCs. Considering the transient efficacy of GPBSCs infusion, allo-HSCT should be taken into consideration as soon as HLH is controlled. Therefore, GPBSCs infusion may play a role in bridging the allo-HSCT, especially for those who didn’t have a previous transplant opportunity.
Except for the one patient mentioned above, who achieved mixed chimerism and suffered severe GVHD causing death, only 6 of the remaining 14 patients developed aGVHD signs, and all of them improved rapidly after symptomatic treatment, even if the amount of CD3 + cells infused was high. None of the 15 patients in the GPBSCs infusion group underwent GVHD prevention treatment. Whether it is DLI or haploid transplantation, although GVL effect is very impressive, the GVHD is also very severe . Although GPBSCs infusion is a kind of transplantation with infused donor cells and chemotherapy, it did not use a pre-treatment regimen with strong immunosuppressive effects similar to haploid transplantation . No severe immunosuppression significantly reduces the incidence and severity of GVHD after infusion. However, considering that there is indeed one patient who died of severe GVHD in this study, although more considerations are of special circumstances, close monitoring of GVHD after infusion is still necessary.
In terms of survival, the survival rate of the GPBSCs infusion group was better than that of the control group within 3 months, but there was no significant difference in the long-term survival. This may suggest that GPBSCs infusion can help with refractory EBV-HLH, but only effects in short terms. Allo-HSCT is still needed to achieve long-term remission . Therefore, we suggest that use GPBSCs as a bridging treatment method to allo-HSCT, for those refractory EBV-HLH patients who do not have a chance to the allo-HSCT before.