#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1169780

use strict;
use warnings;

my @allele = <DATA>;
my @newcounts;
$_ = join '', @allele;

push @newcounts, $& =~ tr/\n// while /^(.*\n)\1*/gm;
print for @newcounts;

__DATA__
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*03:01 
HLA-A*03:01 
HLA-A*03:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:01 
HLA-A*02:03 
HLA-A*02:03 
HLA-A*02:03 
HLA-A*02:03 
HLA-A*02:03 
HLA-A*02:03 
HLA-A*02:03 
HLA-A*02:03