IIA Ten-forms and the Gauge Algebras of Maximal Supergravity Theories
  We show that IIA supergravity can be extended with two independent 10-form potentials. These give rise to a single BPS IIA 9-brane. We investigate the bosonic gauge algebra of both IIA and IIB supergravity in the presence of 10-form potentials and point out an intriguing relation with the symmetry algebra $E_{11}$, which has been conjectured to be the underlying symmetry of string theory/M-theory. 
Eric A. Bergshoeff, Mees de Roo, Sven F. Kerstan, Tomas Ortin, Fabio   Riccioni