Complex sentence: HA1 results from a SNP from a nonimmunogenic allele (KECVLRDDLLEA) to a immunogenic allele (KECVLHDDLLEA) resulting in better peptide binding ability onto the groove of MHC class I molecules of antigen presenting cells.
Split into simpler sentences: HA1 results from a SNP converting the nonimmunogenic allele (KECVLRDDLLEA) to an immunogenic allele (KECVLHDDLLEA). This SNP results in better peptide binding ability to the groove of a particular MHC class I molecules found on antigen presenting cells.