Since the cleavage at the S2′ site by TMPRSS2 necessitates the priming cleavage at S1/S2, the accumulation of FCS mutations in the progeny during the infection in HAE-ALIB15-20 and HAE-ALIKC19 may limit infection of the mut-del1 or mut-del2. This evidence concerns the gene TMPRSS2 and infection.