You probably really want a hash...

#!/usr/bin/perl -w
use strict;

my %lines;

open my $file, "<data.txt" or die "can't open: $!";

while(<$file>)
{
    (my $key, my $stuff) = m/^([^,]*),(.*)/;
    my @data = split(",", $stuff);
    $lines{$key} = \@data;
}

# do something...
print @{$lines{"IL12::1::329"}};
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