  We use Grassmann even spinor oscillators to construct a bosonic higher spin
extension hs(2,2) of the five-dimensional anti-de Sitter algebra SU(2,2), and
show that the gauging of hs(2,2) gives rise to a spectrum S of physical
massless fields with spin s=0,2,4,... that is a UIR of hs(2,2). In addition to
a master gauge field which contains the massless s=2,4,.. fields, we construct
a scalar master field containing the massless s=0 field, the generalized Weyl
tensors and their derivatives. We give the appropriate linearized constraint on
this master scalar field, which together with a linearized curvature constraint
produces the correct linearized field equations. A crucial step in the
construction of the theory is the identification of a central generator K which
is eliminated by means of a coset construction. Its charge vanishes in the
spectrum S, which is the symmetric product of two spin zero doubletons. We
expect our results to pave the way for constructing an interacting theory whose
curvature expansion is dual to a CFT based on higher spin currents formed out
of free doubletons in the large N limit. Thus, extending a recent proposal of
Sundborg (hep-th/0103247), we conjecture that the hs(2,2) gauge theory
describes a truncation of the bosonic massless sector of tensionless
  Type IIB string theory on AdS_5 x S^5 for large N. This implies AdS/CFT
correspondence in a parameter regime where both boundary and bulk theories are
perturbative.
