Beausang John F, Fan H Christina, Sit Rene, Hutchins Maria U, Jirage Kshama, Curtis Rachael, Hutchins Edward, Quake Stephen R, Yabu Julie M
CareDx, 3260 Bayshore Blvd, Brisbane, CA, 94005, USA.
Immumetrix, LLC, 3183 Porter Drive, Palo Alto, CA, 94304, USA.
J Transl Med. 2017 Jan 13;15(1):9. doi: 10.1186/s12967-017-1118-7.
Kidney transplantation is the most effective treatment for end-stage renal disease. Sensitization refers to pre-existing antibodies against human leukocyte antigen (HLA) protein and remains a major barrier to successful transplantation. Despite implementation of desensitization strategies, many candidates fail to respond. Our objective was to determine whether measuring B cell repertoires could differentiate candidates that respond to desensitization therapy.
We developed an assay based on high-throughput DNA sequencing of the variable domain of the heavy chain of immunoglobulin genes to measure changes in B cell repertoires in 19 highly HLA-sensitized kidney transplant candidates undergoing desensitization and 7 controls with low to moderate HLA sensitization levels. Responders to desensitization had a decrease of 5% points or greater in cumulated calculated panel reactive antibody (cPRA) levels, and non-responders had no decrease in cPRA.
Dominant B cell clones were not observed in highly sensitized candidates, suggesting that the B cells responsible for sensitization are either not present in peripheral blood or present at comparable levels to other circulating B cells. Candidates that responded to desensitization therapy had pre-treatment repertoires composed of a larger fraction of class-switched (IgG and IgA) isotypes compared to non-responding candidates. After B cell depleting therapy, the proportion of switched isotypes increased and the mutation frequencies of the remaining non-switched isotypes (IgM and IgD) increased in both responders and non-responders, perhaps representing a shift in the repertoire towards memory B cells or plasmablasts. Conversely, after transplantation, non-switched isotypes with fewer mutations increased, suggesting a shift in the repertoire towards naïve B cells.
Relative abundance of different B cell isotypes is strongly perturbed by desensitization therapy and transplantation, potentially reflecting changes in the relative abundance of memory and naïve B cell compartments. Candidates that responded to therapy experienced similar changes to those that did not respond. Further studies are required to understand differences between these two groups of highly sensitized kidney transplant candidates.
肾移植是终末期肾病最有效的治疗方法。致敏是指预先存在的针对人类白细胞抗原（HLA）蛋白的抗体，仍然是成功移植的主要障碍。尽管实施了脱敏策略，但许多候选者并无反应。我们的目的是确定测量B细胞库是否能够区分对脱敏治疗有反应的候选者。
我们开发了一种基于免疫球蛋白基因重链可变区高通量DNA测序的检测方法，以测量19名接受脱敏治疗的高度HLA致敏肾移植候选者和7名低至中度HLA致敏水平的对照者的B细胞库变化。脱敏治疗的反应者累积计算的群体反应性抗体（cPRA）水平降低5个百分点或更多，无反应者的cPRA没有降低。
在高度致敏的候选者中未观察到优势B细胞克隆，这表明负责致敏的B细胞要么不存在于外周血中，要么与其他循环B细胞处于相当的水平。与无反应的候选者相比，对脱敏治疗有反应的候选者预处理库中由类别转换（IgG和IgA）同种型组成的比例更大。在B细胞清除治疗后，反应者和无反应者中转换同种型的比例均增加，其余未转换同种型（IgM和IgD）的突变频率增加，这可能代表库向记忆B细胞或浆母细胞的转变。相反，移植后，突变较少的未转换同种型增加，这表明库向幼稚B细胞转变。
脱敏治疗和移植会强烈干扰不同B细胞同种型的相对丰度，这可能反映了记忆B细胞和幼稚B细胞区室相对丰度的变化。有反应的候选者和无反应者经历了类似变化，但需要进一步研究以了解这两组高度致敏肾移植候选者之间的差异。
