  For a space X acted by a finite group $\G$, the product space $X^n$ affords a
natural action of the wreath product $\Gn$. In this paper we study the K-groups
$K_{\tG_n}(X^n)$ of $\Gn$-equivariant Clifford supermodules on $X^n$. We show
that $\tFG =\bigoplus_{n\ge 0}K_{\tG_n}(X^n) \otimes \C$ is a Hopf algebra and
it is isomorphic to the Fock space of a twisted Heisenberg algebra. Twisted
vertex operators make a natural appearance. The algebraic structures on $\tFG$,
when $\G$ is trivial and X is a point, specialize to those on a ring of
symmetric functions with the Schur Q-functions as a linear basis. As a
by-product, we present a novel construction of K-theory operations using the
spin representations of the hyperoctahedral groups.
