The Effect Of The Matching Degree Between Allo-NK Cells Receptors And Major Histocompatibility Complex â…  Molecules On The AGVHD

Bone marrow transplantation (BMT) is an effective method in curing the benignand malignant diseases in hematological system and some solid tumors; however, itwas largely limited clinically by some severe complications such as acutegraft-versus-host disease (aGVHD) after the transplantation. Investigators have beenactively searching for the way to relieve the GVHD and consequently increase thesurvival rate. Increasingly study results have shown that, in the allogeneichematopoietic stem cell transplantations, the donors’ allo-reactive natural killercells(allo-NK cells) can get rid of leukemia cells in the recipients and decrease theincidence and severe degree of the GVHD. As the biological effect of the NK cellsdepends on the matching degree between the NK cells receptors and the specificligands, it is supposed that the effect of allo-NK cells on BMT and GVHD wasclosely related to the matching degree between the allo-NK cells receptors andrecipients MHCⅠmolecules. The aims of this study were to elucidate the influence ofthe matching degree between allo-NK cells receptors and major histocompatibilitycomplex I (MHCⅠ)molecules on the GVHD and the underlying mechanism, and tryto explore the feasibility in reducing the complications in bone marrowtransplantations by using the allo-NK cells from a third-party source, such as NK cellsfrom healthy voluntary blood donors.We firstly observed the distribution and the transferring patterns of theexogenous bone marrow cells in MHC molecules fully matching, half matching,totally mismatching recipient mice, respectively. Based on those results, the acuteGVHD model with different MHC matching degrees were established. The bonemarrow cells from the luciferase transgenic mice with a C57BL/6J mouse backgroundwere separated and infused into the irradiated mice, thereafter the distribution pattern of the bone marrow cells in the recipients was observed via in vivo imaging. It isturned out that, exogenous bone marrow cells showed similarly contributioncharacteristic in locations and order in the three kinds of recipients, briefly, the bonemarrow cells firstly distributed in the lungs, and then transferred to the liver, spleen,and mesenteric lymph nodes successively; finally they settled in the hematopoieticmicroenviroment of bone marrow for hematopoietic reconstitution. However, the cellquantity and staying duration were different in mice with various MHC matchingdegree. One hour post the infusion, the exogenous bone marrow cells mainlydistributed in the lungs, and the amount of bone marrow cells in the BALB/c micewere more than those in the CB6F1mice and C57BL/6J mice. Four hours later, theexogenous bone marrow cells were found and gradually increased in the liver andspleen, and the amount of bone marrow cells increased fastestly in the BALB/c micespleen.24hours later, the exogenous bone marrow cells were mainly in the mesenterylymph nodes, the amount of which was the most in BALB/c mice, the least inC57BL/6J mice, and the middle in the CB6F1mice. All the results demonstrated thatthe mismatching degree between the donors cells and the recipients MHC moleculesinfluenced the speed of cells transferring to the lungs, liver, spleen and the mesentery,and restricted the amount and duration of cells staying in these viscera.In order to study the influence of the matching degree between the NK cells andthe receipents MHC molecules on the aGVHD, we firstly established the aGVHDmodels with various MHC matching degree. The intensity of Γ-ray irradiation is themain factor influencing the BMT prognosis and aGVHD incidence. At first, weevaluated the effect of various irradiation intensity and observe the life span, thehematopoietic capacity recovery and chimerism development of the mice with bonemarrow transplantation therapy post radiated by doses of8Gy,6Gy and4Gyrespectively. The radiated CB6F1and BALB/c mice were taken as the recipients,among them the radiated-only mice as the radiated control groups, and the micetransplanted with bone marrow cells from C57BL/6J mice after the radiation as thetransplanted therapy groups. The study results indicatd that the amounts of leukocyte and platelet in the peripheral blood of the mice in the8Gy radiated control groups andtransplanted therapy groups declined notably at+1d, ascended slowly at+7d, and themice all died at+15～+21d with a gomphosis development rate above90%; theamounts of leukocyte and platelet in the transplanted mice post6Gy irradiatedreduced to the lowest level at+7d and then recovered gradually, and the gomphosisdevelopment rate was50%～75%at+2w, exceeding3months’ survival duration; theamounts of leukocyte and platelet in the peripheral blood of the mice in the4Gyradiated control groups and transplanted therapy groups decreased slowly than the8Gy and6Gy groups, recovered gradually at+7d, and the gomphosis developmentrate for the transplanted group was21%～41%at+2W. With an overall considerationon the life span, hematopoietic capacity recovery and the gomphosis development rate,the6Gy was set as the dose for pretreatment in establishing the aGVHD model. Themodel mice presented actively, which were convenient for the samples collected andcould develop a certain gomphosis state.In order to investigate the influence of the matching degree between the allo-NKcells receptors and the recipients MHCⅠmolecules on the aGVHD prognosis, theaGVHD models were established by infusing the bone marrow cells and spleenmononuclear cells from transgenic C57BL/6J mice into irradiated CB6F1andBALB/c mice with intensity of6Gy, respectively. Thereafter, the allo-NK cells fromtransgenic C57BL/6J mice were infused into mice in therapy groups. For CB6F1mice,the mismatching degree between the MHCⅠmolecules and the infused allo-NK cellsreceptors was50%. And for BALB/c mice, the mismatching degree between the MHCⅠmolecules and the infused allo-NK cells receptors was100%. The results indicatedthat, allo-NK cells could enhance gomphosis development and hematopoietic capacityrecovery, reduce the incidence and severity of the aGVHD. The effect was closelyrelated to the matching degree between the allo-NK cells receptors and the recipientsMHCⅠmolecules. For CB6F1mice, although the allo-NK cells infusing couldaccelerate the hematopoietic capacity reconstitution, the difference was of nostatistical significance between therapy and control group. However, for BALB/c mice, allo-NK cells infusing could significantly promote the hematopoietic capacityreconstitution of leucocytes, meanwhile, the clinical manifestations and pathologicalscore of aGVHD were obviously improved, and especially, the pathological changesin the enteric tissue were ameliorated. It was attributable to the reduction of the Th17cells in spleen and the IL-17secretion in blood, as well as enhancement of the Tregcells and the ratio of the Th1/Th2cells reducing in spleen.According to the results of the study, conclusions could be drawn as follows: Theincidence and severity of aGVHD varied in accordance with the matching degreebetween the donors and recipients, and it was partly attributable to the variousdistribution and transferring patterns of the exogenous bone marrow cells in therecipients. Allo-NK cells may increase the ratio of Treg/Th17cells and reduce theradio of Th1/Th2cells in spleen, as well as decrease the IL-17secretion in blood.