What is wrong with the following Common Lisp macro using gensym?

Question

Learning Common Lisp (using GNU CLISP 2.43) .. so might be a noob mistake. Example is the 'print prime numbers between x and y'

(defun is-prime (n)
  (if (< n 2) (return-from is-prime NIL))

  (do ((i 2 (1+ i)))
      ((= i n) T)
    (if (= (mod n i) 0) 
        (return NIL))))

(defun next-prime-after (n)
  (do ((i (1+ n) (1+ i)))
      ((is-prime i) i)))

(defmacro do-primes-v2 ((var start end) &body body)
  `(do ((,var (if (is-prime ,start)
                  ,start
                  (next-prime-after ,start))
              (next-prime-after ,var)))
       ((> ,var ,end))
     ,@body))

(defmacro do-primes-v3 ((var start end) &body body)
  (let ((loop-start (gensym))
        (loop-end (gensym))) 
    `(do ((,loop-start ,start)
          (,loop-end ,end)
          (,var (if (is-prime ,loop-start)
                    ,loop-start
                    (next-prime-after ,loop-start))
                (next-prime-after ,var)))
         ((> ,var ,loop-end))
       ,@body )))

do-primes-v2 works perfectly.

[13]> (do-primes-v2 (p 10 25) (format t "~d " p))
11 13 17 19 23

Next I tried using gensym to avoid naming clashes in macro expansion - do-primes-v3. However I'm stuck with a

*** - EVAL: variable #:G3498 has no value

Tried using macro-expand to see if i could spot the mistake but I can't.

[16]> (macroexpand-1 `(do-primes-v3 (p 10 25) (format t "~d " p)))
(DO
 ((#:G3502 10) (#:G3503 25)
  (P (IF (IS-PRIME #:G3502) #:G3502 (NEXT-PRIME-AFTER #:G3502))
     (NEXT-PRIME-AFTER P)))
 ((> P #:G3503)) (FORMAT T "~d " P)) ;

Answer 1

Use DO* instead of DO.

DO Initializes the bindings in a scope where they are not yet visible. DO* initializes the bindings in a scope where they are visible.

In this particular case var needs to reference the other binding loop-start.