Personal, handwritten response from ''To Kill a Mockingbird'' novelist Harper Lee to a would-be penpal. Lee's southern manners are in fine display here, as she feels compelled to write her admirer, telling him that she can't respond. Letter reads in full: ''I have had a stroke and cannot answer mail. Thanks anyway! Harper Lee''. Large, clear signature in blue ink. Two pages, front and verso, measure 8.5'' x 11''. Expected creases from mailing; near fine.