Analysis of intrapatient heterogeneity uncovers the microevolution of Middle East respiratory syndrome coronavirus

Park, Donghyun; Huh, Hee Jae; Kim, Yeon Jeong; Son, Dae-Soon; Jeon, Hyo-Jeong; Im, Eu-Hyun; Kim, Jong-Won; Lee, Nam Yong; Kang, Eun-Suk; Kang, Cheol In; Chung, Doo Ryeon; Ahn, Jin-Hyun; Peck, Kyong Ran; Choi, Sun Shim; Kim, Yae-Jean; Ki, Chang-Seok; Park, Woong-Yang

Thus, we questioned whether the selection pressure was exerted by a host immune response such as neutralizing antibodies, as previously suggested (Kim et al. 2016c ). In such cases, a reduction in host immune pressure might increase the frequency of the wild type. Four specimens displaying relatively high frequency (i.e., >10%) of the wild type belonged to Patients 77 and 80. We noticed dramatic changes in routine blood test results such as white blood cell (WBC) counts and C-reactive protein (CRP) levels in these patients. We analyzed 19 serial specimens from eight patients. For this, we used normalized WBC count values expressed as a percentage of the first of a series of samples from each patient. Serial samples from Patients 77 and 80 displayed a dramatic decrease in the normalized WBC count and a simultaneous increase in the frequency of the wild-type allele (Supplemental Fig. S4 ). Whereas WBC counts significantly decreased in those patients, the CRP level increased during the period of MERS-CoV infection, indicating an impaired immune response. Although these data are limited owing to the small sample size and the lack of direct measurement of host immunological pressure, our results suggest that the selection pressure exerted by the host immune response might favor variants with reduced affinity to the host receptor; therefore, a reduction in this selection pressure resulted in the expansion of viruses with the wild-type allele. The characterization and quantification of neutralizing antibodies in patients over time is required to determine their association with the mutants and to validate the hypothesis. Moreover, more accurate descriptions of MERS-CoV populations within patients will advance our understanding of the complex molecular evolution of MERS-CoVs.